Best way to reverse a string

Question

I ve just had to write a string reverse function in C  2 0  i e  LINQ not available  and came up with this   public string Reverse string text        char   cArray   text ToCharArray        string reverse   String Empty      for  int i   cArray Length - 1  i  gt  -1  i--                reverse    cArray i             return reverse      Personally I m not crazy about the function and am convinced that there s a better way to do it  Is there

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Best  can depend on many things  but here are few more short alternatives ordered from fast to slow   string s    z a l g  o    pattern       s     lt               lt     P M  p C   p M    1           string s1   string Concat s Reverse                                     o  g l a z     string s2   Microsoft VisualBasic Strings StrReverse s               o g  l a  z     string s3   string Concat StringInfo ParseCombiningCharacters s  Reverse        Select i   gt  StringInfo GetNextTextElement s  i                  o g  l a z      string s4   Regex Replace s  pattern    2   Remove s Length          o g  l a z

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There are various ways to reverse the string  I have shown 3 of them below   -- Using Array Reverse function    private static string ReverseString1 string text                char   rtext   text ToCharArray            Array Reverse rtext           return new string rtext           -- using string only    private static string ReverseString2 string text                String rtext               for  int i   text Length - 1  i  gt   0  i--                        rtext   rtext   text i                     return rtext          -- Using only char array   public static string ReverseString3 string str                char   chars   str ToCharArray            char   rchars   new char chars Length           for  int i   0  j   str Length - 1  i  lt  chars Length  i    j--                        rchars j    chars i                     return new string rchars

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Greg Beech posted an unsafe option that is indeed as fast as it gets  it s an in-place reversal   but  as he indicated in his answer  it s a completely disastrous idea   That said  I m surprised there is so much of a consensus that Array Reverse is the fastest method  There s still an unsafe approach that returns a reversed copy of a string  no in-place reversal shenanigans  significantly faster than the Array Reverse method for small strings   public static unsafe string Reverse string text        int len   text Length          Why allocate a char   array on the heap when you won t use it        outside of this method  Use the stack      char  reversed   stackalloc char len           Avoid bounds-checking performance penalties      fixed  char  str   text                int i   0          int j   i   len - 1          while  i  lt  len                        reversed i      str j--                           Need to use this overload for the System String constructor        as providing just the char  pointer could result in garbage        at the end of the string  no guarantee of null terminator       return new string reversed  0  len       Here are some benchmark results     You can see that the performance gain shrinks and then disappears against the Array Reverse method as the strings get larger  For small- to medium-sized strings  though  it s tough to beat this method

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As simple as this   string x    your string          string x1       for int i   x Length-1   i  gt   0  i--      x1    x i   Console WriteLine  The reverse of the string is  n  0    x1     See the output

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Here a solution that properly reverses the string  Les Mise u0301rables  as  selbare u0301siM seL   This should render just like selbar  siM seL  not selbar  esiM seL  note the position of the accent   as would the result of most implementations based on code units  Array Reverse  etc  or even code points  reversing with special care for surrogate pairs    using System  using System Collections Generic  using System Globalization  using System Linq   public static class Test       private static IEnumerable lt string gt  GraphemeClusters this string s            var enumerator   StringInfo GetTextElementEnumerator s           while enumerator MoveNext                  yield return  string enumerator Current                      private static string ReverseGraphemeClusters this string s            return string Join     s GraphemeClusters   Reverse   ToArray                public static void Main                 var s    Les Mise u0301rables           var r   s ReverseGraphemeClusters            Console WriteLine r              And live running example here  https   ideone com DqAeMJ   It simply uses the  NET API for grapheme cluster iteration  which has been there since ever  but a bit  hidden  from view  it seems

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This is turning out to be a surprisingly tricky question    I would recommend using Array Reverse for most cases as it is coded natively and it is very simple to maintain and understand    It seems to outperform StringBuilder in all the cases I tested     public string Reverse string text       if  text    null  return null         this was posted by petebob as well     char   array   text ToCharArray       Array Reverse array      return new String array       There is a second approach that can be faster for certain string lengths which uses Xor        public static string ReverseXor string s                if  s    null  return null          char   charArray   s ToCharArray            int len   s Length - 1           for  int i   0  i  lt  len  i    len--                        charArray i     charArray len               charArray len     charArray i               charArray i     charArray len                      return new string charArray           Note If you want to support the full Unicode UTF16 charset read this  And use the implementation there instead  It can be further optimized by using one of the above algorithms and running through the string to clean it up after the chars are reversed   Here is a performance comparison between the StringBuilder  Array Reverse and Xor method    using System  using System Collections Generic  using System Linq  using System Text  using System Diagnostics   namespace ConsoleApplication4       class Program               delegate string StringDelegate string s            static void Benchmark string description  StringDelegate d  int times  string text                        Stopwatch sw   new Stopwatch                sw Start                for  int j   0  j  lt  times  j                                  d text                             sw Stop                Console WriteLine   0  Ticks  1    called  2  times    sw ElapsedTicks  description  times                      public static string ReverseXor string s                        char   charArray   s ToCharArray                int len   s Length - 1               for  int i   0  i  lt  len  i    len--                                charArray i     charArray len                   charArray len     charArray i                   charArray i     charArray len                              return new string charArray                      public static string ReverseSB string text                        StringBuilder builder   new StringBuilder text Length               for  int i   text Length - 1  i  gt   0  i--                                builder Append text i                              return builder ToString                       public static string ReverseArray string text                        char   array   text ToCharArray                Array Reverse array               return  new string array                       public static string StringOfLength int length                        Random random   new Random                StringBuilder sb   new StringBuilder                for  int i   0  i  lt  length  i                                  sb Append Convert ToChar Convert ToInt32 Math Floor 26   random NextDouble     65                                return sb ToString                       static void Main string   args                         int   lengths   new int    1 10 15 25 50 75 100 1000 100000                foreach  int l in lengths                                int iterations   10000                  string text   StringOfLength l                   Benchmark String Format  String Builder  Length   0     l   ReverseSB  iterations  text                   Benchmark String Format  Array Reverse  Length   0     l   ReverseArray  iterations  text                   Benchmark String Format  Xor  Length   0     l   ReverseXor  iterations  text                    Console WriteLine                                   Console Read                        Here are the results    26251 Ticks String Builder  Length  1    called 10000 times  33373 Ticks Array Reverse  Length  1    called 10000 times  20162 Ticks Xor  Length  1    called 10000 times   51321 Ticks String Builder  Length  10    called 10000 times  37105 Ticks Array Reverse  Length  10    called 10000 times  23974 Ticks Xor  Length  10    called 10000 times   66570 Ticks String Builder  Length  15    called 10000 times  26027 Ticks Array Reverse  Length  15    called 10000 times  24017 Ticks Xor  Length  15    called 10000 times   101609 Ticks String Builder  Length  25    called 10000 times  28472 Ticks Array Reverse  Length  25    called 10000 times  35355 Ticks Xor  Length  25    called 10000 times   161601 Ticks String Builder  Length  50    called 10000 times  35839 Ticks Array Reverse  Length  50    called 10000 times  51185 Ticks Xor  Length  50    called 10000 times   230898 Ticks String Builder  Length  75    called 10000 times  40628 Ticks Array Reverse  Length  75    called 10000 times  78906 Ticks Xor  Length  75    called 10000 times   312017 Ticks String Builder  Length  100    called 10000 times  52225 Ticks Array Reverse  Length  100    called 10000 times  110195 Ticks Xor  Length  100    called 10000 times   2970691 Ticks String Builder  Length  1000    called 10000 times  292094 Ticks Array Reverse  Length  1000    called 10000 times  846585 Ticks Xor  Length  1000    called 10000 times   305564115 Ticks String Builder  Length  100000    called 10000 times  74884495 Ticks Array Reverse  Length  100000    called 10000 times  125409674 Ticks Xor  Length  100000    called 10000 times    It seems that Xor can be faster for short strings

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Had to submit a recursive example   private static string Reverse string str        if  str IsNullOrEmpty str     str Length    1          return str      else         return str str Length - 1    Reverse str Substring 0  str Length - 1

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Have a look at the wikipedia entry here  They implement the String Reverse extension method  This allows you to write code like this   string s    olleh   s Reverse      They also use the ToCharArray Reverse combination that other answers to this question suggest  The source code looks like this   public static string Reverse this string input        char   chars   input ToCharArray        Array Reverse chars       return new String chars

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Had to submit a recursive example   private static string Reverse string str        if  str IsNullOrEmpty str     str Length    1          return str      else         return str str Length - 1    Reverse str Substring 0  str Length - 1

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Try using Array Reverse   public string Reverse string str        char   array   str ToCharArray        Array Reverse array       return new string array

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Sorry for long post  but this might be interesting  using System  using System Collections Generic  using System Diagnostics  using System Text   namespace ConsoleApplication1       class Program               public static string ReverseUsingArrayClass string text                        char   chars   text ToCharArray                Array Reverse chars               return new string chars                      public static string ReverseUsingCharacterBuffer string text                        char   charArray   new char text Length               int inputStrLength   text Length - 1              for  int idx   0  idx  lt   inputStrLength  idx                                   charArray idx    text inputStrLength - idx                                             return new string charArray                      public static string ReverseUsingStringBuilder string text                        if  string IsNullOrEmpty text                                 return text                             StringBuilder builder   new StringBuilder text Length               for  int i   text Length - 1  i  gt   0  i--                                builder Append text i                               return builder ToString                       private static string ReverseUsingStack string input                        Stack lt char gt  resultStack   new Stack lt char gt                 foreach  char c in input                                resultStack Push c                              StringBuilder sb   new StringBuilder                while  resultStack Count  gt  0                                sb Append resultStack Pop                               return sb ToString                       public static string ReverseUsingXOR string text                        char   charArray   text ToCharArray                int length   text Length - 1              for  int i   0  i  lt  length  i    length--                                charArray i     charArray length                   charArray length     charArray i                   charArray i     charArray length                              return new string charArray                       static void Main string   args                        string testString   string Join      new string                     new string  a   100                    new string  b   101                    new string  c   102                    new string  d   103                                                                                                  int cycleCount   100000               Stopwatch stopwatch   new Stopwatch                stopwatch Start                for  int i   0  i  lt  cycleCount  i                                   ReverseUsingCharacterBuffer testString                             stopwatch Stop                Console WriteLine  ReverseUsingCharacterBuffer      stopwatch ElapsedMilliseconds    ms                 stopwatch Reset                stopwatch Start                for  int i   0  i  lt  cycleCount  i                                   ReverseUsingArrayClass testString                             stopwatch Stop                Console WriteLine  ReverseUsingArrayClass      stopwatch ElapsedMilliseconds    ms                 stopwatch Reset                stopwatch Start                for  int i   0  i  lt  cycleCount  i                                   ReverseUsingStringBuilder testString                             stopwatch Stop                Console WriteLine  ReverseUsingStringBuilder      stopwatch ElapsedMilliseconds    ms                 stopwatch Reset                stopwatch Start                for  int i   0  i  lt  cycleCount  i                                   ReverseUsingStack testString                             stopwatch Stop                Console WriteLine  ReverseUsingStack      stopwatch ElapsedMilliseconds    ms                 stopwatch Reset                stopwatch Start                for  int i   0  i  lt  cycleCount  i                                   ReverseUsingXOR testString                             stopwatch Stop                Console WriteLine  ReverseUsingXOR      stopwatch ElapsedMilliseconds    ms                                    Results    ReverseUsingCharacterBuffer  346ms    ReverseUsingArrayClass  87ms ReverseUsingStringBuilder  824ms ReverseUsingStack  2086ms ReverseUsingXOR  319ms

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It s very simple  static void Reverse                 string str    PankajRawat           var arr   str ToCharArray            for  int i   str Length-1  i  gt   0  i--                        Console Write arr i

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There are various ways to reverse the string  I have shown 3 of them below   -- Using Array Reverse function    private static string ReverseString1 string text                char   rtext   text ToCharArray            Array Reverse rtext           return new string rtext           -- using string only    private static string ReverseString2 string text                String rtext               for  int i   text Length - 1  i  gt   0  i--                        rtext   rtext   text i                     return rtext          -- Using only char array   public static string ReverseString3 string str                char   chars   str ToCharArray            char   rchars   new char chars Length           for  int i   0  j   str Length - 1  i  lt  chars Length  i    j--                        rchars j    chars i                     return new string rchars

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Try using Array Reverse   public string Reverse string str        char   array   str ToCharArray        Array Reverse array       return new string array

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public static string Reverse string input        return string Concat Enumerable Reverse input        Of course you can extend string class with Reverse method  public static class StringExtensions       public static string Reverse this string input                return string Concat Enumerable Reverse input

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As simple as this   string x    your string          string x1       for int i   x Length-1   i  gt   0  i--      x1    x i   Console WriteLine  The reverse of the string is  n  0    x1     See the output

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public static string Reverse  string s         char   charArray   s ToCharArray        Array Reverse  charArray        return new string  charArray

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Firstly you don t need to call ToCharArray as a string can already be indexed as a char array  so this will save you an allocation   The next optimisation is to use a StringBuilder to prevent unnecessary allocations  as strings are immutable  concatenating them makes a copy of the string each time   To further optimise this we pre-set the length of the StringBuilder so it won t need to expand its buffer   public string Reverse string text        if  string IsNullOrEmpty text                 return text             StringBuilder builder   new StringBuilder text Length       for  int i   text Length - 1  i  gt   0  i--                builder Append text i               return builder ToString        Edit  Performance Data  I tested this function and the function using Array Reverse with the following simple program  where Reverse1 is one function and Reverse2 is the other   static void Main string   args        var text    abcdefghijklmnopqrstuvwxyz           pre-jit     text   Reverse1 text        text   Reverse2 text           test     var timer1   Stopwatch StartNew        for  var i   0  i  lt  10000000  i                  text   Reverse1 text              timer1 Stop        Console WriteLine  First   0    timer1 ElapsedMilliseconds        var timer2   Stopwatch StartNew        for  var i   0  i  lt  10000000  i                  text   Reverse2 text              timer2 Stop        Console WriteLine  Second   0    timer2 ElapsedMilliseconds        Console ReadLine        It turns out that for short strings the Array Reverse method is around twice as quick as the one above  and for longer strings the difference is even more pronounced  So given that the Array Reverse method is both simpler and faster I d recommend you use that rather than this one  I leave this one up here just to show that it isn t the way you should do it  much to my surprise

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Better way  depends on what is more important to you in your situation  performance  elegance  maintainability etc   Anyway  here s an approach using Array Reverse   string inputString  The quick brown fox jumps over the lazy dog    char   charArray   inputString ToCharArray     Array Reverse charArray     string reversed   new string charArray

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private static string Reverse string str                        string revStr   string Empty              for  int i   str Length - 1  i  gt   0  i--                                revStr    str i  ToString                              return revStr              Faster than above method  private static string ReverseEx string str                        char   chrArray   str ToCharArray                int len   chrArray Length - 1              char rev    n               for  int i   0  i  lt   len 2  i                                  rev   chrArray i                   chrArray i    chrArray len - i                   chrArray len - i    rev                            return new string chrArray

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Ok  in the interest of  don t repeat yourself   I offer the following solution   public string Reverse string text       return Microsoft VisualBasic Strings StrReverse text       My understanding is that this implementation  available by default in VB NET  properly handles Unicode characters

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If the string contains Unicode data  strictly speaking  non-BMP characters  the other methods that have been posted will corrupt it  because you cannot swap the order of high and low surrogate code units when reversing the string   More information about this can be found on my blog    The following code sample will correctly reverse a string that contains non-BMP characters  e g     U00010380 U00010381   Ugaritic Letter Alpa  Ugaritic Letter Beta    public static string Reverse this string input        if  input    null          throw new ArgumentNullException  input            allocate a buffer to hold the output     char   output   new char input Length       for  int outputIndex   0  inputIndex   input Length - 1  outputIndex  lt  input Length  outputIndex    inputIndex--                   check for surrogate pair         if  input inputIndex   gt   0xDC00  amp  amp  input inputIndex   lt   0xDFFF  amp  amp              inputIndex  gt  0  amp  amp  input inputIndex - 1   gt   0xD800  amp  amp  input inputIndex - 1   lt   0xDBFF                           preserve the order of the surrogate pair code units             output outputIndex   1    input inputIndex               output outputIndex    input inputIndex - 1               outputIndex                inputIndex--                    else                       output outputIndex    input inputIndex                        return new string output

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here is a unicode safe version of the function  written as an extension that will safely handle unicode   It is close to the marked complete answer  but will not throw exceptions for  Invalid high surrogate character    public static class StringExtensions       public static string Reverse this string s                var info   new StringInfo s           var charArray   new char s Length           var teIndices   StringInfo ParseCombiningCharacters s  Reverse             int j   0          foreach var i in  teIndices                        if  char IsHighSurrogate s i                                  charArray j    s i                   j                    charArray j    s i 1                             else                               charArray j    s i                             j                       return new string charArray

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public string Reverse string input        char   output   new char input Length        int forwards   0      int backwards   input Length - 1       do               output forwards    input backwards           output backwards    input forwards        while   forwards  lt   --backwards        return new String output      public string DotNetReverse string input        char   toReverse   input ToCharArray        Array Reverse toReverse       return new String toReverse      public string NaiveReverse string input        char   outputArray   new char input Length       for  int i   0  i  lt  input Length  i                  outputArray i    input input Length - 1 - i              return new String outputArray          public string RecursiveReverse string input        return RecursiveReverseHelper input  0  input Length - 1      public string RecursiveReverseHelper string input  int startIndex   int endIndex        if  startIndex    endIndex                return      input startIndex              if  endIndex - startIndex    1                return      input endIndex    input startIndex              return input endIndex    RecursiveReverseHelper input  startIndex   1  endIndex - 1    input startIndex       void Main         int   sizes   new int     10  100  1000  10000        for int sizeIndex   0  sizeIndex  lt  sizes Length  sizeIndex                  string holaMundo                for int i   0  i  lt  sizes sizeIndex   i   5                           holaMundo     ABCDE                      string Format   n     For size   0       n   sizes sizeIndex   Dump             string odnuMaloh   DotNetReverse holaMundo            var stopWatch   Stopwatch StartNew            string result   NaiveReverse holaMundo             Naive Ticks      stopWatch ElapsedTicks  Dump             stopWatch Restart            result   Reverse holaMundo             Efficient linear Ticks      stopWatch ElapsedTicks  Dump             stopWatch Restart            result   RecursiveReverse holaMundo             Recursive Ticks      stopWatch ElapsedTicks  Dump             stopWatch Restart            result   DotNetReverse holaMundo             DotNet Reverse Ticks      stopWatch ElapsedTicks  Dump              Output  For size  10  Naive Ticks  1 Efficient linear Ticks  0 Recursive Ticks  2 DotNet Reverse Ticks  1   For size  100  Naive Ticks  2 Efficient linear Ticks  1 Recursive Ticks  12 DotNet Reverse Ticks  1   For size  1000  Naive Ticks  5 Efficient linear Ticks  2 Recursive Ticks  358 DotNet Reverse Ticks  9   For size  10000  Naive Ticks  32 Efficient linear Ticks  28 Recursive Ticks  84808 DotNet Reverse Ticks  33

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I was asked a similar question in interview   This was my response  although it is probably not as fast in performance as other answers   My question was phrased as  Make a class that can have a method to print a string backwards    using System  using System Collections Generic  using System Linq   namespace BackwardsTest       class PrintBackwards               public static void print string param                        if  param    null    param Length    0                                Console WriteLine  string is null                    return                            List lt char gt  list   new List lt char gt                 string returned   null              foreach char d in param                                list Add d                             for int i   list Count    i  gt  0  i--                                returned   returned   list list Count - 1                   list RemoveAt list Count - 1                             Console WriteLine returned                       class Program               static void Main string   args                        string test    I want to print backwards               PrintBackwards print test               System Threading Thread Sleep 5000

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Have a look at the wikipedia entry here  They implement the String Reverse extension method  This allows you to write code like this   string s    olleh   s Reverse      They also use the ToCharArray Reverse combination that other answers to this question suggest  The source code looks like this   public static string Reverse this string input        char   chars   input ToCharArray        Array Reverse chars       return new String chars

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First of all what you have to understand is that str   will resize your string memory to make space for 1 extra char  This is fine  but if you have  say  a book with 1000 pages that you want to reverse  this will take very long to execute   The solution that some people might suggest is using StringBuilder  What string builder does when you perform a    is that it allocates much larger chunks of memory to hold the new character so that it does not need to do a reallocation every time you add a char    If you really want a fast and minimal solution I d suggest the following               char   chars   new char str Length               for  int i   str Length - 1  j   0  i  gt   0  --i    j                                chars j    str i                             str   new String chars     In this solution there is one initial memory allocation when the char   is initialized and one allocation when the string constructor builds the string from the char array    On my system I ran a test for you that reverses a string of 2 750 000 characters  Here are the results for 10 executions   StringBuilder  190K - 200K ticks  Char Array  130K - 160K ticks  I also ran a test for normal String    but I abandoned it after 10 minutes with no output   However  I also noticed that for smaller strings the StringBuilder is faster  so you will have to decide on the implementation based on the input   Cheers

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How about       private string Reverse string stringToReverse                char   rev   stringToReverse Reverse   ToArray            return new string rev

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How about use Substring  static string ReverseString string text        string sub           int indexCount   text Length - 1      for  int i   indexCount  i  gt  -1  i--                sub   sub   text Substring i  1             return sub

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How about use Substring  static string ReverseString string text        string sub           int indexCount   text Length - 1      for  int i   indexCount  i  gt  -1  i--                sub   sub   text Substring i  1             return sub

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The easy and nice answer is using the Extension Method   static class ExtentionMethodCollection       public static string Inverse this string  base                return new string  base Reverse   ToArray               and here s the output    string Answer    12345  Inverse          54321

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First of all what you have to understand is that str   will resize your string memory to make space for 1 extra char  This is fine  but if you have  say  a book with 1000 pages that you want to reverse  this will take very long to execute   The solution that some people might suggest is using StringBuilder  What string builder does when you perform a    is that it allocates much larger chunks of memory to hold the new character so that it does not need to do a reallocation every time you add a char    If you really want a fast and minimal solution I d suggest the following               char   chars   new char str Length               for  int i   str Length - 1  j   0  i  gt   0  --i    j                                chars j    str i                             str   new String chars     In this solution there is one initial memory allocation when the char   is initialized and one allocation when the string constructor builds the string from the char array    On my system I ran a test for you that reverses a string of 2 750 000 characters  Here are the results for 10 executions   StringBuilder  190K - 200K ticks  Char Array  130K - 160K ticks  I also ran a test for normal String    but I abandoned it after 10 minutes with no output   However  I also noticed that for smaller strings the StringBuilder is faster  so you will have to decide on the implementation based on the input   Cheers

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string A   null    a now is reversed and you can use it A   SimulateStrReverse StrReverse  your string     public static class SimulateStrReverse       public static string StrReverse string expression                if  string IsNullOrEmpty expression               return string Empty           string reversedString   string Empty          for  int charIndex   expression Length - 1  charIndex  gt   0  charIndex--                        reversedString    expression charIndex                     return reversedString

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Here a solution that properly reverses the string  Les Mise u0301rables  as  selbare u0301siM seL   This should render just like selbar  siM seL  not selbar  esiM seL  note the position of the accent   as would the result of most implementations based on code units  Array Reverse  etc  or even code points  reversing with special care for surrogate pairs    using System  using System Collections Generic  using System Globalization  using System Linq   public static class Test       private static IEnumerable lt string gt  GraphemeClusters this string s            var enumerator   StringInfo GetTextElementEnumerator s           while enumerator MoveNext                  yield return  string enumerator Current                      private static string ReverseGraphemeClusters this string s            return string Join     s GraphemeClusters   Reverse   ToArray                public static void Main                 var s    Les Mise u0301rables           var r   s ReverseGraphemeClusters            Console WriteLine r              And live running example here  https   ideone com DqAeMJ   It simply uses the  NET API for grapheme cluster iteration  which has been there since ever  but a bit  hidden  from view  it seems

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If someone asks about string reverse  the intension could be to find out whether you know any bitwise operation like XOR  In C  you have Array Reverse function  however  you can do using simple XOR operation in few lines of code minimal      public static string MyReverse string s                char   charArray   s ToCharArray            int bgn   -1          int end   s Length          while   bgn  lt  --end                        charArray bgn     charArray end               charArray end     charArray bgn               charArray bgn     charArray end                     return new string charArray

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If it ever came up in an interview and you were told you can t use Array Reverse  i think this might be one of the fastest   It does not create new strings and iterates only over half of the array  i e O n 2  iterations       public static string ReverseString string stringToReverse                char   charArray   stringToReverse ToCharArray            int len   charArray Length-1          int mid   len   2           for  int i   0  i  lt  mid  i                          char tmp   charArray i               charArray i    charArray len - i               charArray len - i    tmp                    return new string charArray

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public static string Reverse2 string x                        char   charArray   new char x Length               int len   x Length - 1              for  int i   0  i  lt   len  i                    charArray i    x len - i               return new string charArray

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Simplest way   string reversed   new string text Reverse   ToArray

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public static string Reverse  string s         char   charArray   s ToCharArray        Array Reverse  charArray        return new string  charArray

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string original    Stack Overflow       string reversed   new string original Reverse   ToArray

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Better way  depends on what is more important to you in your situation  performance  elegance  maintainability etc   Anyway  here s an approach using Array Reverse   string inputString  The quick brown fox jumps over the lazy dog    char   charArray   inputString ToCharArray     Array Reverse charArray     string reversed   new string charArray

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Sorry for long post  but this might be interesting  using System  using System Collections Generic  using System Diagnostics  using System Text   namespace ConsoleApplication1       class Program               public static string ReverseUsingArrayClass string text                        char   chars   text ToCharArray                Array Reverse chars               return new string chars                      public static string ReverseUsingCharacterBuffer string text                        char   charArray   new char text Length               int inputStrLength   text Length - 1              for  int idx   0  idx  lt   inputStrLength  idx                                   charArray idx    text inputStrLength - idx                                             return new string charArray                      public static string ReverseUsingStringBuilder string text                        if  string IsNullOrEmpty text                                 return text                             StringBuilder builder   new StringBuilder text Length               for  int i   text Length - 1  i  gt   0  i--                                builder Append text i                               return builder ToString                       private static string ReverseUsingStack string input                        Stack lt char gt  resultStack   new Stack lt char gt                 foreach  char c in input                                resultStack Push c                              StringBuilder sb   new StringBuilder                while  resultStack Count  gt  0                                sb Append resultStack Pop                               return sb ToString                       public static string ReverseUsingXOR string text                        char   charArray   text ToCharArray                int length   text Length - 1              for  int i   0  i  lt  length  i    length--                                charArray i     charArray length                   charArray length     charArray i                   charArray i     charArray length                              return new string charArray                       static void Main string   args                        string testString   string Join      new string                     new string  a   100                    new string  b   101                    new string  c   102                    new string  d   103                                                                                                  int cycleCount   100000               Stopwatch stopwatch   new Stopwatch                stopwatch Start                for  int i   0  i  lt  cycleCount  i                                   ReverseUsingCharacterBuffer testString                             stopwatch Stop                Console WriteLine  ReverseUsingCharacterBuffer      stopwatch ElapsedMilliseconds    ms                 stopwatch Reset                stopwatch Start                for  int i   0  i  lt  cycleCount  i                                   ReverseUsingArrayClass testString                             stopwatch Stop                Console WriteLine  ReverseUsingArrayClass      stopwatch ElapsedMilliseconds    ms                 stopwatch Reset                stopwatch Start                for  int i   0  i  lt  cycleCount  i                                   ReverseUsingStringBuilder testString                             stopwatch Stop                Console WriteLine  ReverseUsingStringBuilder      stopwatch ElapsedMilliseconds    ms                 stopwatch Reset                stopwatch Start                for  int i   0  i  lt  cycleCount  i                                   ReverseUsingStack testString                             stopwatch Stop                Console WriteLine  ReverseUsingStack      stopwatch ElapsedMilliseconds    ms                 stopwatch Reset                stopwatch Start                for  int i   0  i  lt  cycleCount  i                                   ReverseUsingXOR testString                             stopwatch Stop                Console WriteLine  ReverseUsingXOR      stopwatch ElapsedMilliseconds    ms                                    Results    ReverseUsingCharacterBuffer  346ms    ReverseUsingArrayClass  87ms ReverseUsingStringBuilder  824ms ReverseUsingStack  2086ms ReverseUsingXOR  319ms

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If you can use LINQ   NET Framework 3 5   than following one liner will give you short code  Don t forget to add using System Linq  to have access to Enumerable Reverse   public string ReverseString string srtVarable        return new string srtVarable Reverse   ToArray         Notes    not the fastest version - according to   Martin Niederl 5 7 times slower than the fastest choice here  this code as many other options completely ignores all sorts of multi-character combinations  so limit usage to homework assignments and strings which do not contain such characters  See another answer in this question for implementation that correctly handles such combinations

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Sorry for long post  but this might be interesting  using System  using System Collections Generic  using System Diagnostics  using System Text   namespace ConsoleApplication1       class Program               public static string ReverseUsingArrayClass string text                        char   chars   text ToCharArray                Array Reverse chars               return new string chars                      public static string ReverseUsingCharacterBuffer string text                        char   charArray   new char text Length               int inputStrLength   text Length - 1              for  int idx   0  idx  lt   inputStrLength  idx                                   charArray idx    text inputStrLength - idx                                             return new string charArray                      public static string ReverseUsingStringBuilder string text                        if  string IsNullOrEmpty text                                 return text                             StringBuilder builder   new StringBuilder text Length               for  int i   text Length - 1  i  gt   0  i--                                builder Append text i                               return builder ToString                       private static string ReverseUsingStack string input                        Stack lt char gt  resultStack   new Stack lt char gt                 foreach  char c in input                                resultStack Push c                              StringBuilder sb   new StringBuilder                while  resultStack Count  gt  0                                sb Append resultStack Pop                               return sb ToString                       public static string ReverseUsingXOR string text                        char   charArray   text ToCharArray                int length   text Length - 1              for  int i   0  i  lt  length  i    length--                                charArray i     charArray length                   charArray length     charArray i                   charArray i     charArray length                              return new string charArray                       static void Main string   args                        string testString   string Join      new string                     new string  a   100                    new string  b   101                    new string  c   102                    new string  d   103                                                                                                  int cycleCount   100000               Stopwatch stopwatch   new Stopwatch                stopwatch Start                for  int i   0  i  lt  cycleCount  i                                   ReverseUsingCharacterBuffer testString                             stopwatch Stop                Console WriteLine  ReverseUsingCharacterBuffer      stopwatch ElapsedMilliseconds    ms                 stopwatch Reset                stopwatch Start                for  int i   0  i  lt  cycleCount  i                                   ReverseUsingArrayClass testString                             stopwatch Stop                Console WriteLine  ReverseUsingArrayClass      stopwatch ElapsedMilliseconds    ms                 stopwatch Reset                stopwatch Start                for  int i   0  i  lt  cycleCount  i                                   ReverseUsingStringBuilder testString                             stopwatch Stop                Console WriteLine  ReverseUsingStringBuilder      stopwatch ElapsedMilliseconds    ms                 stopwatch Reset                stopwatch Start                for  int i   0  i  lt  cycleCount  i                                   ReverseUsingStack testString                             stopwatch Stop                Console WriteLine  ReverseUsingStack      stopwatch ElapsedMilliseconds    ms                 stopwatch Reset                stopwatch Start                for  int i   0  i  lt  cycleCount  i                                   ReverseUsingXOR testString                             stopwatch Stop                Console WriteLine  ReverseUsingXOR      stopwatch ElapsedMilliseconds    ms                                    Results    ReverseUsingCharacterBuffer  346ms    ReverseUsingArrayClass  87ms ReverseUsingStringBuilder  824ms ReverseUsingStack  2086ms ReverseUsingXOR  319ms

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Starting with  NET Core 2 1 there is a new way to reverse a string using the string Create method   Note that this solution does not handle Unicode combining characters etc  correctly  as  Les Mise u0301rables  would be converted to  selbar  siM seL   The the other answers for a better solution   public static string Reverse string input        return string Create lt string gt  input Length  input   chars  state    gt                state AsSpan   CopyTo chars           chars Reverse                This essentially copies the characters of input to a new string and reverses the new string in-place   Why is string Create useful   When we create a string from an existing array  a new internal array is allocated and the values are copied  Otherwise  it would be possible to mutate a string after its creation  in a safe environment   That is  in the following snippet we have to allocate an array of length 10 twice  one as the buffer and one as the string s internal array   var chars   new char 10      set array values var str   new string chars     string Create essentially allows us to manipulate the internal array during creation time of the string  This is  we do not need a buffer anymore and can therefore avoid allocating that one char array   Steve Gordon has written about it in more detail here  There is also an article on MSDN   How to use string Create   public static string Create lt TState gt  int length  TState state  SpanAction lt char  TState gt  action     The method takes three parameters    The length of the string to create  the data you want to use to dynamically create the new string  and a delegate that creates the final string from the data  where the first parameter points to the internal char array of the new string and the second is the data  state  you passed to string Create    Inside the delegate we can specify how the new string is created from the data  In our case  we just copy the characters of the input string to the Span used by the new string  Then we reverse the Span and hence the whole string is reversed   Benchmarks  To compare my proposed way of reversing a string with the accepted answer  I have written two benchmarks using BenchmarkDotNet   public class StringExtensions       public static string ReverseWithArray string input                var charArray   input ToCharArray            Array Reverse charArray           return new string charArray              public static string ReverseWithStringCreate string input                return string Create input Length  input   chars  state    gt                        state AsSpan   CopyTo chars               chars Reverse                          MemoryDiagnoser  public class StringReverseBenchmarks       private string input        Params 10  100  1000       public int InputLength   get  set           GlobalSetup      public void SetInput                    Creates a random string of the given length         this input   RandomStringGenerator GetString InputLength               Benchmark Baseline   true       public string WithReverseArray     gt  StringExtensions ReverseWithArray input         Benchmark      public string WithStringCreate     gt  StringExtensions ReverseWithStringCreate input       Here are the results on my machine     Method             InputLength           Mean        Error      StdDev    Gen 0   Allocated     ----------------   -----------   -----------    ---------    --------    -----    --------      WithReverseArray   10               45 464 ns    0 4836 ns   0 4524 ns   0 0610        96 B     WithStringCreate   10               39 749 ns    0 3206 ns   0 2842 ns   0 0305        48 B                                                                                                     WithReverseArray   100             175 162 ns    2 8766 ns   2 2458 ns   0 2897       456 B     WithStringCreate   100             125 284 ns    2 4657 ns   2 0590 ns   0 1473       232 B                                                                                                     WithReverseArray   1000          1 523 544 ns    9 8808 ns   8 7591 ns   2 5768      4056 B     WithStringCreate   1000          1 078 957 ns   10 2948 ns   9 6298 ns   1 2894      2032 B     As you can see  with ReverseWithStringCreate we allocate only half of the memory used by the ReverseWithArray method

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Sorry for posting on this old thread  I am practicing some code for an interview   This was what I came up with for C   My first version before refactoring was horrible   static String Reverse2 string str        int strLen   str Length  elem   strLen - 1      char   charA   new char strLen        for  int i   0  i  lt  strLen  i                  charA elem    str i           elem--             return new String charA       In Contrast to the Array Reverse method below  it appears faster with 12 characters or less in the string  After 13 characters  the Array Reverse starts to get faster  and it eventually dominates pretty heavily on speed  I just wanted to point out approximately where the speed starts to change   static String Reverse string str             char   charA   str ToCharArray         Array Reverse charA        return new String charA       At 100 characters in the string  it is faster than my version x 4  However  if I knew that the strings would always be less than 13 characters  I would use the one I made    Testing was done with Stopwatch and 5000000 iterations  Also  I m not sure if my version handles Surrogates or combined character situations with Unicode encoding

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Firstly you don t need to call ToCharArray as a string can already be indexed as a char array  so this will save you an allocation   The next optimisation is to use a StringBuilder to prevent unnecessary allocations  as strings are immutable  concatenating them makes a copy of the string each time   To further optimise this we pre-set the length of the StringBuilder so it won t need to expand its buffer   public string Reverse string text        if  string IsNullOrEmpty text                 return text             StringBuilder builder   new StringBuilder text Length       for  int i   text Length - 1  i  gt   0  i--                builder Append text i               return builder ToString        Edit  Performance Data  I tested this function and the function using Array Reverse with the following simple program  where Reverse1 is one function and Reverse2 is the other   static void Main string   args        var text    abcdefghijklmnopqrstuvwxyz           pre-jit     text   Reverse1 text        text   Reverse2 text           test     var timer1   Stopwatch StartNew        for  var i   0  i  lt  10000000  i                  text   Reverse1 text              timer1 Stop        Console WriteLine  First   0    timer1 ElapsedMilliseconds        var timer2   Stopwatch StartNew        for  var i   0  i  lt  10000000  i                  text   Reverse2 text              timer2 Stop        Console WriteLine  Second   0    timer2 ElapsedMilliseconds        Console ReadLine        It turns out that for short strings the Array Reverse method is around twice as quick as the one above  and for longer strings the difference is even more pronounced  So given that the Array Reverse method is both simpler and faster I d recommend you use that rather than this one  I leave this one up here just to show that it isn t the way you should do it  much to my surprise

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string A   null    a now is reversed and you can use it A   SimulateStrReverse StrReverse  your string     public static class SimulateStrReverse       public static string StrReverse string expression                if  string IsNullOrEmpty expression               return string Empty           string reversedString   string Empty          for  int charIndex   expression Length - 1  charIndex  gt   0  charIndex--                        reversedString    expression charIndex                     return reversedString

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static void Main string   args        string str           string reverse           Console WriteLine  Enter the value to reverse        str   Console ReadLine        int length   0      length   str Length - 1      while length  gt   0                reverse   reverse   str length           length--            Console Write  Reverse string is  0    reverse       Console ReadKey

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This is the code used for reverse string   public Static void main        string text    Test Text       Console Writeline RevestString text      public Static string RevestString string text       char   textToChar   text ToCharArray        string result  string Empty      int length   textToChar  Length      for  int i   length  i  gt  0  --i      result    textToChar i - 1       return result

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Since I like a couple of the answers - one for using string Create and therefore high performance and low allocation and another for correctness - using the StringInfo class  I decided a combined approach is needed  This is the ultimate string reversal method     private static string ReverseString string str                return string Create str Length  str   chars  state    gt                        var enumerator   StringInfo GetTextElementEnumerator state               var position   state Length              while  enumerator MoveNext                                  var cluster     string enumerator Current  AsSpan                    cluster CopyTo chars Slice position - cluster Length                    position -  cluster Length                                    There s an even better way using a method of the StringInfo class which skips a lot of string allocations by the Enumerator by returning just the indexes   private static string ReverseString string str                return string Create str Length  str   chars  state    gt                        var position   0              var indexes   StringInfo ParseCombiningCharacters state      skips string creation             var stateSpan   state AsSpan                for  int len   indexes Length  i   len - 1  i  gt   0  i--                                var index   indexes i                   var spanLength   i    len - 1   state Length - index   indexes i   1  - index                  stateSpan Slice index  spanLength  CopyTo chars Slice position                    position    spanLength                                    Some benchmarks compared to the LINQ solution   String length 20   LINQ                       Mean  2 355 5 ns   Allocated  1440 B string Create              Mean    851 0 ns   Allocated   720 B string Create with indexes Mean    466 4 ns   Allocated   168 B  String length 450   LINQ                          Mean  34 33 us   Allocated  22 98 KB string Create                 Mean    19 13 us   Allocated  14 98 KB string Create with indexes    Mean    10 32 us   Allocated  2 69 KB

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If you want to play a really dangerous game  then this is by far the fastest way there is  around four times faster than the Array Reverse method   It s an in-place reverse using pointers   Note that I really do not recommend this for any use  ever  have a look here for some reasons why you should not use this method   but it s just interesting to see that it can be done  and that strings aren t really immutable once you turn on unsafe code   public static unsafe string Reverse string text        if  string IsNullOrEmpty text                 return text             fixed  char  pText   text                char  pStart   pText          char  pEnd   pText   text Length - 1          for  int i   text Length   2  i  gt   0  i--                        char temp    pStart               pStart      pEnd               pEnd--   temp                     return text

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Better way  depends on what is more important to you in your situation  performance  elegance  maintainability etc   Anyway  here s an approach using Array Reverse   string inputString  The quick brown fox jumps over the lazy dog    char   charArray   inputString ToCharArray     Array Reverse charArray     string reversed   new string charArray

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Handles all type of unicode characters   using System Globalization       public static string ReverseString this string content             var textElementEnumerator   StringInfo GetTextElementEnumerator content            var SbBuilder   new StringBuilder content Length            while  textElementEnumerator MoveNext                  SbBuilder Insert 0  textElementEnumerator GetTextElement                        return SbBuilder ToString

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public string rev string str        if  str Length  lt   0          return string Empty      else         return str str Length-1   rev str Substring 0 str Length-1

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If you want to play a really dangerous game  then this is by far the fastest way there is  around four times faster than the Array Reverse method   It s an in-place reverse using pointers   Note that I really do not recommend this for any use  ever  have a look here for some reasons why you should not use this method   but it s just interesting to see that it can be done  and that strings aren t really immutable once you turn on unsafe code   public static unsafe string Reverse string text        if  string IsNullOrEmpty text                 return text             fixed  char  pText   text                char  pStart   pText          char  pEnd   pText   text Length - 1          for  int i   text Length   2  i  gt   0  i--                        char temp    pStart               pStart      pEnd               pEnd--   temp                     return text

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If you want to play a really dangerous game  then this is by far the fastest way there is  around four times faster than the Array Reverse method   It s an in-place reverse using pointers   Note that I really do not recommend this for any use  ever  have a look here for some reasons why you should not use this method   but it s just interesting to see that it can be done  and that strings aren t really immutable once you turn on unsafe code   public static unsafe string Reverse string text        if  string IsNullOrEmpty text                 return text             fixed  char  pText   text                char  pStart   pText          char  pEnd   pText   text Length - 1          for  int i   text Length   2  i  gt   0  i--                        char temp    pStart               pStart      pEnd               pEnd--   temp                     return text

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The easy and nice answer is using the Extension Method   static class ExtentionMethodCollection       public static string Inverse this string  base                return new string  base Reverse   ToArray               and here s the output    string Answer    12345  Inverse          54321

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SELECT REVERSE  somestring    Done

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using System  using System Collections Generic  using System Linq  using System Text  using System Threading Tasks   namespace ConsoleApplication1       class Program                    public static string ReverseString string str                        int totalLength   str Length              int iCount   0              string strRev   string Empty              iCount   totalLength              while  iCount    0                                iCount--                  strRev    str iCount                              return strRev                    static void Main string   args                        string str    Punit Pandya               string strResult   ReverseString str               Console WriteLine strResult               Console ReadLine

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It s very simple  static void Reverse                 string str    PankajRawat           var arr   str ToCharArray            for  int i   str Length-1  i  gt   0  i--                        Console Write arr i

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Try using Array Reverse   public string Reverse string str        char   array   str ToCharArray        Array Reverse array       return new string array

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If you have a string that only contains ASCII characters  you can use this method       public static string ASCIIReverse string s                byte   reversed   new byte s Length            int k   0          for  int i   s Length - 1  i  gt   0  i--                        reversed k       byte s i                      return Encoding ASCII GetString reversed

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public static string Reverse  string s         char   charArray   s ToCharArray        Array Reverse  charArray        return new string  charArray

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This is turning out to be a surprisingly tricky question    I would recommend using Array Reverse for most cases as it is coded natively and it is very simple to maintain and understand    It seems to outperform StringBuilder in all the cases I tested     public string Reverse string text       if  text    null  return null         this was posted by petebob as well     char   array   text ToCharArray       Array Reverse array      return new String array       There is a second approach that can be faster for certain string lengths which uses Xor        public static string ReverseXor string s                if  s    null  return null          char   charArray   s ToCharArray            int len   s Length - 1           for  int i   0  i  lt  len  i    len--                        charArray i     charArray len               charArray len     charArray i               charArray i     charArray len                      return new string charArray           Note If you want to support the full Unicode UTF16 charset read this  And use the implementation there instead  It can be further optimized by using one of the above algorithms and running through the string to clean it up after the chars are reversed   Here is a performance comparison between the StringBuilder  Array Reverse and Xor method    using System  using System Collections Generic  using System Linq  using System Text  using System Diagnostics   namespace ConsoleApplication4       class Program               delegate string StringDelegate string s            static void Benchmark string description  StringDelegate d  int times  string text                        Stopwatch sw   new Stopwatch                sw Start                for  int j   0  j  lt  times  j                                  d text                             sw Stop                Console WriteLine   0  Ticks  1    called  2  times    sw ElapsedTicks  description  times                      public static string ReverseXor string s                        char   charArray   s ToCharArray                int len   s Length - 1               for  int i   0  i  lt  len  i    len--                                charArray i     charArray len                   charArray len     charArray i                   charArray i     charArray len                              return new string charArray                      public static string ReverseSB string text                        StringBuilder builder   new StringBuilder text Length               for  int i   text Length - 1  i  gt   0  i--                                builder Append text i                              return builder ToString                       public static string ReverseArray string text                        char   array   text ToCharArray                Array Reverse array               return  new string array                       public static string StringOfLength int length                        Random random   new Random                StringBuilder sb   new StringBuilder                for  int i   0  i  lt  length  i                                  sb Append Convert ToChar Convert ToInt32 Math Floor 26   random NextDouble     65                                return sb ToString                       static void Main string   args                         int   lengths   new int    1 10 15 25 50 75 100 1000 100000                foreach  int l in lengths                                int iterations   10000                  string text   StringOfLength l                   Benchmark String Format  String Builder  Length   0     l   ReverseSB  iterations  text                   Benchmark String Format  Array Reverse  Length   0     l   ReverseArray  iterations  text                   Benchmark String Format  Xor  Length   0     l   ReverseXor  iterations  text                    Console WriteLine                                   Console Read                        Here are the results    26251 Ticks String Builder  Length  1    called 10000 times  33373 Ticks Array Reverse  Length  1    called 10000 times  20162 Ticks Xor  Length  1    called 10000 times   51321 Ticks String Builder  Length  10    called 10000 times  37105 Ticks Array Reverse  Length  10    called 10000 times  23974 Ticks Xor  Length  10    called 10000 times   66570 Ticks String Builder  Length  15    called 10000 times  26027 Ticks Array Reverse  Length  15    called 10000 times  24017 Ticks Xor  Length  15    called 10000 times   101609 Ticks String Builder  Length  25    called 10000 times  28472 Ticks Array Reverse  Length  25    called 10000 times  35355 Ticks Xor  Length  25    called 10000 times   161601 Ticks String Builder  Length  50    called 10000 times  35839 Ticks Array Reverse  Length  50    called 10000 times  51185 Ticks Xor  Length  50    called 10000 times   230898 Ticks String Builder  Length  75    called 10000 times  40628 Ticks Array Reverse  Length  75    called 10000 times  78906 Ticks Xor  Length  75    called 10000 times   312017 Ticks String Builder  Length  100    called 10000 times  52225 Ticks Array Reverse  Length  100    called 10000 times  110195 Ticks Xor  Length  100    called 10000 times   2970691 Ticks String Builder  Length  1000    called 10000 times  292094 Ticks Array Reverse  Length  1000    called 10000 times  846585 Ticks Xor  Length  1000    called 10000 times   305564115 Ticks String Builder  Length  100000    called 10000 times  74884495 Ticks Array Reverse  Length  100000    called 10000 times  125409674 Ticks Xor  Length  100000    called 10000 times    It seems that Xor can be faster for short strings

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private static string Reverse string str                        string revStr   string Empty              for  int i   str Length - 1  i  gt   0  i--                                revStr    str i  ToString                              return revStr              Faster than above method  private static string ReverseEx string str                        char   chrArray   str ToCharArray                int len   chrArray Length - 1              char rev    n               for  int i   0  i  lt   len 2  i                                  rev   chrArray i                   chrArray i    chrArray len - i                   chrArray len - i    rev                            return new string chrArray

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public static string reverse string s         string r           for  int i   s Length  i  gt  0  i--  r    s i - 1       return r

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I was asked a similar question in interview   This was my response  although it is probably not as fast in performance as other answers   My question was phrased as  Make a class that can have a method to print a string backwards    using System  using System Collections Generic  using System Linq   namespace BackwardsTest       class PrintBackwards               public static void print string param                        if  param    null    param Length    0                                Console WriteLine  string is null                    return                            List lt char gt  list   new List lt char gt                 string returned   null              foreach char d in param                                list Add d                             for int i   list Count    i  gt  0  i--                                returned   returned   list list Count - 1                   list RemoveAt list Count - 1                             Console WriteLine returned                       class Program               static void Main string   args                        string test    I want to print backwards               PrintBackwards print test               System Threading Thread Sleep 5000

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static void Main string   args        string str           string reverse           Console WriteLine  Enter the value to reverse        str   Console ReadLine        int length   0      length   str Length - 1      while length  gt   0                reverse   reverse   str length           length--            Console Write  Reverse string is  0    reverse       Console ReadKey

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Had to submit a recursive example   private static string Reverse string str        if  str IsNullOrEmpty str     str Length    1          return str      else         return str str Length - 1    Reverse str Substring 0  str Length - 1

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Sorry for posting on this old thread  I am practicing some code for an interview   This was what I came up with for C   My first version before refactoring was horrible   static String Reverse2 string str        int strLen   str Length  elem   strLen - 1      char   charA   new char strLen        for  int i   0  i  lt  strLen  i                  charA elem    str i           elem--             return new String charA       In Contrast to the Array Reverse method below  it appears faster with 12 characters or less in the string  After 13 characters  the Array Reverse starts to get faster  and it eventually dominates pretty heavily on speed  I just wanted to point out approximately where the speed starts to change   static String Reverse string str             char   charA   str ToCharArray         Array Reverse charA        return new String charA       At 100 characters in the string  it is faster than my version x 4  However  if I knew that the strings would always be less than 13 characters  I would use the one I made    Testing was done with Stopwatch and 5000000 iterations  Also  I m not sure if my version handles Surrogates or combined character situations with Unicode encoding

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If the string contains Unicode data  strictly speaking  non-BMP characters  the other methods that have been posted will corrupt it  because you cannot swap the order of high and low surrogate code units when reversing the string   More information about this can be found on my blog    The following code sample will correctly reverse a string that contains non-BMP characters  e g     U00010380 U00010381   Ugaritic Letter Alpa  Ugaritic Letter Beta    public static string Reverse this string input        if  input    null          throw new ArgumentNullException  input            allocate a buffer to hold the output     char   output   new char input Length       for  int outputIndex   0  inputIndex   input Length - 1  outputIndex  lt  input Length  outputIndex    inputIndex--                   check for surrogate pair         if  input inputIndex   gt   0xDC00  amp  amp  input inputIndex   lt   0xDFFF  amp  amp              inputIndex  gt  0  amp  amp  input inputIndex - 1   gt   0xD800  amp  amp  input inputIndex - 1   lt   0xDBFF                           preserve the order of the surrogate pair code units             output outputIndex   1    input inputIndex               output outputIndex    input inputIndex - 1               outputIndex                inputIndex--                    else                       output outputIndex    input inputIndex                        return new string output

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Had to submit a recursive example   private static string Reverse string str        if  str IsNullOrEmpty str     str Length    1          return str      else         return str str Length - 1    Reverse str Substring 0  str Length - 1

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Have a look at the wikipedia entry here  They implement the String Reverse extension method  This allows you to write code like this   string s    olleh   s Reverse      They also use the ToCharArray Reverse combination that other answers to this question suggest  The source code looks like this   public static string Reverse this string input        char   chars   input ToCharArray        Array Reverse chars       return new String chars

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Firstly you don t need to call ToCharArray as a string can already be indexed as a char array  so this will save you an allocation   The next optimisation is to use a StringBuilder to prevent unnecessary allocations  as strings are immutable  concatenating them makes a copy of the string each time   To further optimise this we pre-set the length of the StringBuilder so it won t need to expand its buffer   public string Reverse string text        if  string IsNullOrEmpty text                 return text             StringBuilder builder   new StringBuilder text Length       for  int i   text Length - 1  i  gt   0  i--                builder Append text i               return builder ToString        Edit  Performance Data  I tested this function and the function using Array Reverse with the following simple program  where Reverse1 is one function and Reverse2 is the other   static void Main string   args        var text    abcdefghijklmnopqrstuvwxyz           pre-jit     text   Reverse1 text        text   Reverse2 text           test     var timer1   Stopwatch StartNew        for  var i   0  i  lt  10000000  i                  text   Reverse1 text              timer1 Stop        Console WriteLine  First   0    timer1 ElapsedMilliseconds        var timer2   Stopwatch StartNew        for  var i   0  i  lt  10000000  i                  text   Reverse2 text              timer2 Stop        Console WriteLine  Second   0    timer2 ElapsedMilliseconds        Console ReadLine        It turns out that for short strings the Array Reverse method is around twice as quick as the one above  and for longer strings the difference is even more pronounced  So given that the Array Reverse method is both simpler and faster I d recommend you use that rather than this one  I leave this one up here just to show that it isn t the way you should do it  much to my surprise

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Simplest way   string reversed   new string text Reverse   ToArray

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here is a unicode safe version of the function  written as an extension that will safely handle unicode   It is close to the marked complete answer  but will not throw exceptions for  Invalid high surrogate character    public static class StringExtensions       public static string Reverse this string s                var info   new StringInfo s           var charArray   new char s Length           var teIndices   StringInfo ParseCombiningCharacters s  Reverse             int j   0          foreach var i in  teIndices                        if  char IsHighSurrogate s i                                  charArray j    s i                   j                    charArray j    s i 1                             else                               charArray j    s i                             j                       return new string charArray

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Stack-based solution       public static string Reverse string text                var stack   new Stack lt char gt  text           var array   new char stack Count            int i   0          while  stack Count    0                        array i      stack Pop                       return new string array           Or       public static string Reverse string text                var stack   new Stack lt char gt  text           return string Join     stack

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public static string reverse string s         string r           for  int i   s Length  i  gt  0  i--  r    s i - 1       return r

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public string Reverse string input        char   output   new char input Length        int forwards   0      int backwards   input Length - 1       do               output forwards    input backwards           output backwards    input forwards        while   forwards  lt   --backwards        return new String output      public string DotNetReverse string input        char   toReverse   input ToCharArray        Array Reverse toReverse       return new String toReverse      public string NaiveReverse string input        char   outputArray   new char input Length       for  int i   0  i  lt  input Length  i                  outputArray i    input input Length - 1 - i              return new String outputArray          public string RecursiveReverse string input        return RecursiveReverseHelper input  0  input Length - 1      public string RecursiveReverseHelper string input  int startIndex   int endIndex        if  startIndex    endIndex                return      input startIndex              if  endIndex - startIndex    1                return      input endIndex    input startIndex              return input endIndex    RecursiveReverseHelper input  startIndex   1  endIndex - 1    input startIndex       void Main         int   sizes   new int     10  100  1000  10000        for int sizeIndex   0  sizeIndex  lt  sizes Length  sizeIndex                  string holaMundo                for int i   0  i  lt  sizes sizeIndex   i   5                           holaMundo     ABCDE                      string Format   n     For size   0       n   sizes sizeIndex   Dump             string odnuMaloh   DotNetReverse holaMundo            var stopWatch   Stopwatch StartNew            string result   NaiveReverse holaMundo             Naive Ticks      stopWatch ElapsedTicks  Dump             stopWatch Restart            result   Reverse holaMundo             Efficient linear Ticks      stopWatch ElapsedTicks  Dump             stopWatch Restart            result   RecursiveReverse holaMundo             Recursive Ticks      stopWatch ElapsedTicks  Dump             stopWatch Restart            result   DotNetReverse holaMundo             DotNet Reverse Ticks      stopWatch ElapsedTicks  Dump              Output  For size  10  Naive Ticks  1 Efficient linear Ticks  0 Recursive Ticks  2 DotNet Reverse Ticks  1   For size  100  Naive Ticks  2 Efficient linear Ticks  1 Recursive Ticks  12 DotNet Reverse Ticks  1   For size  1000  Naive Ticks  5 Efficient linear Ticks  2 Recursive Ticks  358 DotNet Reverse Ticks  9   For size  10000  Naive Ticks  32 Efficient linear Ticks  28 Recursive Ticks  84808 DotNet Reverse Ticks  33

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If the string contains Unicode data  strictly speaking  non-BMP characters  the other methods that have been posted will corrupt it  because you cannot swap the order of high and low surrogate code units when reversing the string   More information about this can be found on my blog    The following code sample will correctly reverse a string that contains non-BMP characters  e g     U00010380 U00010381   Ugaritic Letter Alpa  Ugaritic Letter Beta    public static string Reverse this string input        if  input    null          throw new ArgumentNullException  input            allocate a buffer to hold the output     char   output   new char input Length       for  int outputIndex   0  inputIndex   input Length - 1  outputIndex  lt  input Length  outputIndex    inputIndex--                   check for surrogate pair         if  input inputIndex   gt   0xDC00  amp  amp  input inputIndex   lt   0xDFFF  amp  amp              inputIndex  gt  0  amp  amp  input inputIndex - 1   gt   0xD800  amp  amp  input inputIndex - 1   lt   0xDBFF                           preserve the order of the surrogate pair code units             output outputIndex   1    input inputIndex               output outputIndex    input inputIndex - 1               outputIndex                inputIndex--                    else                       output outputIndex    input inputIndex                        return new string output

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Don t bother with a function  just do it in place   Note  The second line will throw an argument exception in the Immediate window of some VS versions   string s    Blah   s   new string s ToCharArray   Reverse   ToArray

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Handles all type of unicode characters   using System Globalization       public static string ReverseString this string content             var textElementEnumerator   StringInfo GetTextElementEnumerator content            var SbBuilder   new StringBuilder content Length            while  textElementEnumerator MoveNext                  SbBuilder Insert 0  textElementEnumerator GetTextElement                        return SbBuilder ToString

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Reverse a String without even using a new string  Lets say  String input     Mark Henry     Just to convert into char array  One can simply take input in char array  Char   array   input toCharArray input   int a   input length   for int i 0  i lt  array length 2 -1    i          array i    array i    array a       array a    array i  - array a       array i    array i  - array a--

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If the string contains Unicode data  strictly speaking  non-BMP characters  the other methods that have been posted will corrupt it  because you cannot swap the order of high and low surrogate code units when reversing the string   More information about this can be found on my blog    The following code sample will correctly reverse a string that contains non-BMP characters  e g     U00010380 U00010381   Ugaritic Letter Alpa  Ugaritic Letter Beta    public static string Reverse this string input        if  input    null          throw new ArgumentNullException  input            allocate a buffer to hold the output     char   output   new char input Length       for  int outputIndex   0  inputIndex   input Length - 1  outputIndex  lt  input Length  outputIndex    inputIndex--                   check for surrogate pair         if  input inputIndex   gt   0xDC00  amp  amp  input inputIndex   lt   0xDFFF  amp  amp              inputIndex  gt  0  amp  amp  input inputIndex - 1   gt   0xD800  amp  amp  input inputIndex - 1   lt   0xDBFF                           preserve the order of the surrogate pair code units             output outputIndex   1    input inputIndex               output outputIndex    input inputIndex - 1               outputIndex                inputIndex--                    else                       output outputIndex    input inputIndex                        return new string output

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Reverse a String without even using a new string  Lets say  String input     Mark Henry     Just to convert into char array  One can simply take input in char array  Char   array   input toCharArray input   int a   input length   for int i 0  i lt  array length 2 -1    i          array i    array i    array a       array a    array i  - array a       array i    array i  - array a--

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SELECT REVERSE  somestring    Done

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Greg Beech posted an unsafe option that is indeed as fast as it gets  it s an in-place reversal   but  as he indicated in his answer  it s a completely disastrous idea   That said  I m surprised there is so much of a consensus that Array Reverse is the fastest method  There s still an unsafe approach that returns a reversed copy of a string  no in-place reversal shenanigans  significantly faster than the Array Reverse method for small strings   public static unsafe string Reverse string text        int len   text Length          Why allocate a char   array on the heap when you won t use it        outside of this method  Use the stack      char  reversed   stackalloc char len           Avoid bounds-checking performance penalties      fixed  char  str   text                int i   0          int j   i   len - 1          while  i  lt  len                        reversed i      str j--                           Need to use this overload for the System String constructor        as providing just the char  pointer could result in garbage        at the end of the string  no guarantee of null terminator       return new string reversed  0  len       Here are some benchmark results     You can see that the performance gain shrinks and then disappears against the Array Reverse method as the strings get larger  For small- to medium-sized strings  though  it s tough to beat this method

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Stack-based solution       public static string Reverse string text                var stack   new Stack lt char gt  text           var array   new char stack Count            int i   0          while  stack Count    0                        array i      stack Pop                       return new string array           Or       public static string Reverse string text                var stack   new Stack lt char gt  text           return string Join     stack

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Have a look at the wikipedia entry here  They implement the String Reverse extension method  This allows you to write code like this   string s    olleh   s Reverse      They also use the ToCharArray Reverse combination that other answers to this question suggest  The source code looks like this   public static string Reverse this string input        char   chars   input ToCharArray        Array Reverse chars       return new String chars

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This is turning out to be a surprisingly tricky question    I would recommend using Array Reverse for most cases as it is coded natively and it is very simple to maintain and understand    It seems to outperform StringBuilder in all the cases I tested     public string Reverse string text       if  text    null  return null         this was posted by petebob as well     char   array   text ToCharArray       Array Reverse array      return new String array       There is a second approach that can be faster for certain string lengths which uses Xor        public static string ReverseXor string s                if  s    null  return null          char   charArray   s ToCharArray            int len   s Length - 1           for  int i   0  i  lt  len  i    len--                        charArray i     charArray len               charArray len     charArray i               charArray i     charArray len                      return new string charArray           Note If you want to support the full Unicode UTF16 charset read this  And use the implementation there instead  It can be further optimized by using one of the above algorithms and running through the string to clean it up after the chars are reversed   Here is a performance comparison between the StringBuilder  Array Reverse and Xor method    using System  using System Collections Generic  using System Linq  using System Text  using System Diagnostics   namespace ConsoleApplication4       class Program               delegate string StringDelegate string s            static void Benchmark string description  StringDelegate d  int times  string text                        Stopwatch sw   new Stopwatch                sw Start                for  int j   0  j  lt  times  j                                  d text                             sw Stop                Console WriteLine   0  Ticks  1    called  2  times    sw ElapsedTicks  description  times                      public static string ReverseXor string s                        char   charArray   s ToCharArray                int len   s Length - 1               for  int i   0  i  lt  len  i    len--                                charArray i     charArray len                   charArray len     charArray i                   charArray i     charArray len                              return new string charArray                      public static string ReverseSB string text                        StringBuilder builder   new StringBuilder text Length               for  int i   text Length - 1  i  gt   0  i--                                builder Append text i                              return builder ToString                       public static string ReverseArray string text                        char   array   text ToCharArray                Array Reverse array               return  new string array                       public static string StringOfLength int length                        Random random   new Random                StringBuilder sb   new StringBuilder                for  int i   0  i  lt  length  i                                  sb Append Convert ToChar Convert ToInt32 Math Floor 26   random NextDouble     65                                return sb ToString                       static void Main string   args                         int   lengths   new int    1 10 15 25 50 75 100 1000 100000                foreach  int l in lengths                                int iterations   10000                  string text   StringOfLength l                   Benchmark String Format  String Builder  Length   0     l   ReverseSB  iterations  text                   Benchmark String Format  Array Reverse  Length   0     l   ReverseArray  iterations  text                   Benchmark String Format  Xor  Length   0     l   ReverseXor  iterations  text                    Console WriteLine                                   Console Read                        Here are the results    26251 Ticks String Builder  Length  1    called 10000 times  33373 Ticks Array Reverse  Length  1    called 10000 times  20162 Ticks Xor  Length  1    called 10000 times   51321 Ticks String Builder  Length  10    called 10000 times  37105 Ticks Array Reverse  Length  10    called 10000 times  23974 Ticks Xor  Length  10    called 10000 times   66570 Ticks String Builder  Length  15    called 10000 times  26027 Ticks Array Reverse  Length  15    called 10000 times  24017 Ticks Xor  Length  15    called 10000 times   101609 Ticks String Builder  Length  25    called 10000 times  28472 Ticks Array Reverse  Length  25    called 10000 times  35355 Ticks Xor  Length  25    called 10000 times   161601 Ticks String Builder  Length  50    called 10000 times  35839 Ticks Array Reverse  Length  50    called 10000 times  51185 Ticks Xor  Length  50    called 10000 times   230898 Ticks String Builder  Length  75    called 10000 times  40628 Ticks Array Reverse  Length  75    called 10000 times  78906 Ticks Xor  Length  75    called 10000 times   312017 Ticks String Builder  Length  100    called 10000 times  52225 Ticks Array Reverse  Length  100    called 10000 times  110195 Ticks Xor  Length  100    called 10000 times   2970691 Ticks String Builder  Length  1000    called 10000 times  292094 Ticks Array Reverse  Length  1000    called 10000 times  846585 Ticks Xor  Length  1000    called 10000 times   305564115 Ticks String Builder  Length  100000    called 10000 times  74884495 Ticks Array Reverse  Length  100000    called 10000 times  125409674 Ticks Xor  Length  100000    called 10000 times    It seems that Xor can be faster for short strings

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public string rev string str        if  str Length  lt   0          return string Empty      else         return str str Length-1   rev str Substring 0 str Length-1

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Best  can depend on many things  but here are few more short alternatives ordered from fast to slow   string s    z a l g  o    pattern       s     lt               lt     P M  p C   p M    1           string s1   string Concat s Reverse                                     o  g l a z     string s2   Microsoft VisualBasic Strings StrReverse s               o g  l a  z     string s3   string Concat StringInfo ParseCombiningCharacters s  Reverse        Select i   gt  StringInfo GetNextTextElement s  i                  o g  l a z      string s4   Regex Replace s  pattern    2   Remove s Length          o g  l a z

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Better way  depends on what is more important to you in your situation  performance  elegance  maintainability etc   Anyway  here s an approach using Array Reverse   string inputString  The quick brown fox jumps over the lazy dog    char   charArray   inputString ToCharArray     Array Reverse charArray     string reversed   new string charArray

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public static string Reverse  string s         char   charArray   s ToCharArray        Array Reverse  charArray        return new string  charArray

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Firstly you don t need to call ToCharArray as a string can already be indexed as a char array  so this will save you an allocation   The next optimisation is to use a StringBuilder to prevent unnecessary allocations  as strings are immutable  concatenating them makes a copy of the string each time   To further optimise this we pre-set the length of the StringBuilder so it won t need to expand its buffer   public string Reverse string text        if  string IsNullOrEmpty text                 return text             StringBuilder builder   new StringBuilder text Length       for  int i   text Length - 1  i  gt   0  i--                builder Append text i               return builder ToString        Edit  Performance Data  I tested this function and the function using Array Reverse with the following simple program  where Reverse1 is one function and Reverse2 is the other   static void Main string   args        var text    abcdefghijklmnopqrstuvwxyz           pre-jit     text   Reverse1 text        text   Reverse2 text           test     var timer1   Stopwatch StartNew        for  var i   0  i  lt  10000000  i                  text   Reverse1 text              timer1 Stop        Console WriteLine  First   0    timer1 ElapsedMilliseconds        var timer2   Stopwatch StartNew        for  var i   0  i  lt  10000000  i                  text   Reverse2 text              timer2 Stop        Console WriteLine  Second   0    timer2 ElapsedMilliseconds        Console ReadLine        It turns out that for short strings the Array Reverse method is around twice as quick as the one above  and for longer strings the difference is even more pronounced  So given that the Array Reverse method is both simpler and faster I d recommend you use that rather than this one  I leave this one up here just to show that it isn t the way you should do it  much to my surprise

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How about       private string Reverse string stringToReverse                char   rev   stringToReverse Reverse   ToArray            return new string rev

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Ok  in the interest of  don t repeat yourself   I offer the following solution   public string Reverse string text       return Microsoft VisualBasic Strings StrReverse text       My understanding is that this implementation  available by default in VB NET  properly handles Unicode characters

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Using LINQ s Aggregate function  string s    Karthik U   s   s Aggregate new StringBuilder     o  p    gt  o Insert 0  p   ToString

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If you can use LINQ   NET Framework 3 5   than following one liner will give you short code  Don t forget to add using System Linq  to have access to Enumerable Reverse   public string ReverseString string srtVarable        return new string srtVarable Reverse   ToArray         Notes    not the fastest version - according to   Martin Niederl 5 7 times slower than the fastest choice here  this code as many other options completely ignores all sorts of multi-character combinations  so limit usage to homework assignments and strings which do not contain such characters  See another answer in this question for implementation that correctly handles such combinations

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using System  using System Collections Generic  using System Linq  using System Text  using System Threading Tasks   namespace ConsoleApplication1       class Program                    public static string ReverseString string str                        int totalLength   str Length              int iCount   0              string strRev   string Empty              iCount   totalLength              while  iCount    0                                iCount--                  strRev    str iCount                              return strRev                    static void Main string   args                        string str    Punit Pandya               string strResult   ReverseString str               Console WriteLine strResult               Console ReadLine

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Sorry for long post  but this might be interesting  using System  using System Collections Generic  using System Diagnostics  using System Text   namespace ConsoleApplication1       class Program               public static string ReverseUsingArrayClass string text                        char   chars   text ToCharArray                Array Reverse chars               return new string chars                      public static string ReverseUsingCharacterBuffer string text                        char   charArray   new char text Length               int inputStrLength   text Length - 1              for  int idx   0  idx  lt   inputStrLength  idx                                   charArray idx    text inputStrLength - idx                                             return new string charArray                      public static string ReverseUsingStringBuilder string text                        if  string IsNullOrEmpty text                                 return text                             StringBuilder builder   new StringBuilder text Length               for  int i   text Length - 1  i  gt   0  i--                                builder Append text i                               return builder ToString                       private static string ReverseUsingStack string input                        Stack lt char gt  resultStack   new Stack lt char gt                 foreach  char c in input                                resultStack Push c                              StringBuilder sb   new StringBuilder                while  resultStack Count  gt  0                                sb Append resultStack Pop                               return sb ToString                       public static string ReverseUsingXOR string text                        char   charArray   text ToCharArray                int length   text Length - 1              for  int i   0  i  lt  length  i    length--                                charArray i     charArray length                   charArray length     charArray i                   charArray i     charArray length                              return new string charArray                       static void Main string   args                        string testString   string Join      new string                     new string  a   100                    new string  b   101                    new string  c   102                    new string  d   103                                                                                                  int cycleCount   100000               Stopwatch stopwatch   new Stopwatch                stopwatch Start                for  int i   0  i  lt  cycleCount  i                                   ReverseUsingCharacterBuffer testString                             stopwatch Stop                Console WriteLine  ReverseUsingCharacterBuffer      stopwatch ElapsedMilliseconds    ms                 stopwatch Reset                stopwatch Start                for  int i   0  i  lt  cycleCount  i                                   ReverseUsingArrayClass testString                             stopwatch Stop                Console WriteLine  ReverseUsingArrayClass      stopwatch ElapsedMilliseconds    ms                 stopwatch Reset                stopwatch Start                for  int i   0  i  lt  cycleCount  i                                   ReverseUsingStringBuilder testString                             stopwatch Stop                Console WriteLine  ReverseUsingStringBuilder      stopwatch ElapsedMilliseconds    ms                 stopwatch Reset                stopwatch Start                for  int i   0  i  lt  cycleCount  i                                   ReverseUsingStack testString                             stopwatch Stop                Console WriteLine  ReverseUsingStack      stopwatch ElapsedMilliseconds    ms                 stopwatch Reset                stopwatch Start                for  int i   0  i  lt  cycleCount  i                                   ReverseUsingXOR testString                             stopwatch Stop                Console WriteLine  ReverseUsingXOR      stopwatch ElapsedMilliseconds    ms                                    Results    ReverseUsingCharacterBuffer  346ms    ReverseUsingArrayClass  87ms ReverseUsingStringBuilder  824ms ReverseUsingStack  2086ms ReverseUsingXOR  319ms

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If it ever came up in an interview and you were told you can t use Array Reverse  i think this might be one of the fastest   It does not create new strings and iterates only over half of the array  i e O n 2  iterations       public static string ReverseString string stringToReverse                char   charArray   stringToReverse ToCharArray            int len   charArray Length-1          int mid   len   2           for  int i   0  i  lt  mid  i                          char tmp   charArray i               charArray i    charArray len - i               charArray len - i    tmp                    return new string charArray

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Since I like a couple of the answers - one for using string Create and therefore high performance and low allocation and another for correctness - using the StringInfo class  I decided a combined approach is needed  This is the ultimate string reversal method     private static string ReverseString string str                return string Create str Length  str   chars  state    gt                        var enumerator   StringInfo GetTextElementEnumerator state               var position   state Length              while  enumerator MoveNext                                  var cluster     string enumerator Current  AsSpan                    cluster CopyTo chars Slice position - cluster Length                    position -  cluster Length                                    There s an even better way using a method of the StringInfo class which skips a lot of string allocations by the Enumerator by returning just the indexes   private static string ReverseString string str                return string Create str Length  str   chars  state    gt                        var position   0              var indexes   StringInfo ParseCombiningCharacters state      skips string creation             var stateSpan   state AsSpan                for  int len   indexes Length  i   len - 1  i  gt   0  i--                                var index   indexes i                   var spanLength   i    len - 1   state Length - index   indexes i   1  - index                  stateSpan Slice index  spanLength  CopyTo chars Slice position                    position    spanLength                                    Some benchmarks compared to the LINQ solution   String length 20   LINQ                       Mean  2 355 5 ns   Allocated  1440 B string Create              Mean    851 0 ns   Allocated   720 B string Create with indexes Mean    466 4 ns   Allocated   168 B  String length 450   LINQ                          Mean  34 33 us   Allocated  22 98 KB string Create                 Mean    19 13 us   Allocated  14 98 KB string Create with indexes    Mean    10 32 us   Allocated  2 69 KB

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This is turning out to be a surprisingly tricky question    I would recommend using Array Reverse for most cases as it is coded natively and it is very simple to maintain and understand    It seems to outperform StringBuilder in all the cases I tested     public string Reverse string text       if  text    null  return null         this was posted by petebob as well     char   array   text ToCharArray       Array Reverse array      return new String array       There is a second approach that can be faster for certain string lengths which uses Xor        public static string ReverseXor string s                if  s    null  return null          char   charArray   s ToCharArray            int len   s Length - 1           for  int i   0  i  lt  len  i    len--                        charArray i     charArray len               charArray len     charArray i               charArray i     charArray len                      return new string charArray           Note If you want to support the full Unicode UTF16 charset read this  And use the implementation there instead  It can be further optimized by using one of the above algorithms and running through the string to clean it up after the chars are reversed   Here is a performance comparison between the StringBuilder  Array Reverse and Xor method    using System  using System Collections Generic  using System Linq  using System Text  using System Diagnostics   namespace ConsoleApplication4       class Program               delegate string StringDelegate string s            static void Benchmark string description  StringDelegate d  int times  string text                        Stopwatch sw   new Stopwatch                sw Start                for  int j   0  j  lt  times  j                                  d text                             sw Stop                Console WriteLine   0  Ticks  1    called  2  times    sw ElapsedTicks  description  times                      public static string ReverseXor string s                        char   charArray   s ToCharArray                int len   s Length - 1               for  int i   0  i  lt  len  i    len--                                charArray i     charArray len                   charArray len     charArray i                   charArray i     charArray len                              return new string charArray                      public static string ReverseSB string text                        StringBuilder builder   new StringBuilder text Length               for  int i   text Length - 1  i  gt   0  i--                                builder Append text i                              return builder ToString                       public static string ReverseArray string text                        char   array   text ToCharArray                Array Reverse array               return  new string array                       public static string StringOfLength int length                        Random random   new Random                StringBuilder sb   new StringBuilder                for  int i   0  i  lt  length  i                                  sb Append Convert ToChar Convert ToInt32 Math Floor 26   random NextDouble     65                                return sb ToString                       static void Main string   args                         int   lengths   new int    1 10 15 25 50 75 100 1000 100000                foreach  int l in lengths                                int iterations   10000                  string text   StringOfLength l                   Benchmark String Format  String Builder  Length   0     l   ReverseSB  iterations  text                   Benchmark String Format  Array Reverse  Length   0     l   ReverseArray  iterations  text                   Benchmark String Format  Xor  Length   0     l   ReverseXor  iterations  text                    Console WriteLine                                   Console Read                        Here are the results    26251 Ticks String Builder  Length  1    called 10000 times  33373 Ticks Array Reverse  Length  1    called 10000 times  20162 Ticks Xor  Length  1    called 10000 times   51321 Ticks String Builder  Length  10    called 10000 times  37105 Ticks Array Reverse  Length  10    called 10000 times  23974 Ticks Xor  Length  10    called 10000 times   66570 Ticks String Builder  Length  15    called 10000 times  26027 Ticks Array Reverse  Length  15    called 10000 times  24017 Ticks Xor  Length  15    called 10000 times   101609 Ticks String Builder  Length  25    called 10000 times  28472 Ticks Array Reverse  Length  25    called 10000 times  35355 Ticks Xor  Length  25    called 10000 times   161601 Ticks String Builder  Length  50    called 10000 times  35839 Ticks Array Reverse  Length  50    called 10000 times  51185 Ticks Xor  Length  50    called 10000 times   230898 Ticks String Builder  Length  75    called 10000 times  40628 Ticks Array Reverse  Length  75    called 10000 times  78906 Ticks Xor  Length  75    called 10000 times   312017 Ticks String Builder  Length  100    called 10000 times  52225 Ticks Array Reverse  Length  100    called 10000 times  110195 Ticks Xor  Length  100    called 10000 times   2970691 Ticks String Builder  Length  1000    called 10000 times  292094 Ticks Array Reverse  Length  1000    called 10000 times  846585 Ticks Xor  Length  1000    called 10000 times   305564115 Ticks String Builder  Length  100000    called 10000 times  74884495 Ticks Array Reverse  Length  100000    called 10000 times  125409674 Ticks Xor  Length  100000    called 10000 times    It seems that Xor can be faster for short strings

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I ve made a C  port from Microsoft VisualBasic Strings  I m not sure why they keep such useful functions  from VB  outside the System String in Framework  but still under Microsoft VisualBasic  Same scenario for financial functions  e g  Microsoft VisualBasic Financial Pmt      public static string StrReverse this string expression        if   expression    null           return          int srcIndex       var length   expression Length      if  length    0          return            CONSIDER  Get System String to add a surrogate aware Reverse method        Detect if there are any graphemes that need special handling     for  srcIndex   0  srcIndex  lt   length - 1  srcIndex                  var ch   expression srcIndex           var uc   char GetUnicodeCategory ch           if  uc    UnicodeCategory Surrogate    uc    UnicodeCategory NonSpacingMark    uc    UnicodeCategory SpacingCombiningMark    uc    UnicodeCategory EnclosingMark                          Need to use special handling             return InternalStrReverse expression  srcIndex  length                        var chars   expression ToCharArray        Array Reverse chars       return new string chars          lt remarks gt This routine handles reversing Strings containing graphemes     GRAPHEME  a text element that is displayed as a single character lt  remarks gt  private static string InternalStrReverse string expression  int srcIndex  int length          This code can only be hit one time     var sb   new StringBuilder length    Length   length         var textEnum   StringInfo GetTextElementEnumerator expression  srcIndex          Init enumerator position     if   textEnum MoveNext                  return                var lastSrcIndex   0      var destIndex   length - 1         Copy up the first surrogate found     while  lastSrcIndex  lt  srcIndex                sb destIndex    expression lastSrcIndex           destIndex -  1          lastSrcIndex    1               Now iterate through the text elements and copy them to the reversed string     var nextSrcIndex   textEnum ElementIndex       while  destIndex  gt   0                srcIndex   nextSrcIndex             Move to next element         nextSrcIndex    textEnum MoveNext      textEnum ElementIndex   length          lastSrcIndex   nextSrcIndex - 1           while  lastSrcIndex  gt   srcIndex                        sb destIndex    expression lastSrcIndex               destIndex -  1              lastSrcIndex -  1                       return sb ToString

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This is the code used for reverse string   public Static void main        string text    Test Text       Console Writeline RevestString text      public Static string RevestString string text       char   textToChar   text ToCharArray        string result  string Empty      int length   textToChar  Length      for  int i   length  i  gt  0  --i      result    textToChar i - 1       return result

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If you have a string that only contains ASCII characters  you can use this method       public static string ASCIIReverse string s                byte   reversed   new byte s Length            int k   0          for  int i   s Length - 1  i  gt   0  i--                        reversed k       byte s i                      return Encoding ASCII GetString reversed

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If someone asks about string reverse  the intension could be to find out whether you know any bitwise operation like XOR  In C  you have Array Reverse function  however  you can do using simple XOR operation in few lines of code minimal      public static string MyReverse string s                char   charArray   s ToCharArray            int bgn   -1          int end   s Length          while   bgn  lt  --end                        charArray bgn     charArray end               charArray end     charArray bgn               charArray bgn     charArray end                     return new string charArray

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string original    Stack Overflow       string reversed   new string original Reverse   ToArray

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Don t bother with a function  just do it in place   Note  The second line will throw an argument exception in the Immediate window of some VS versions   string s    Blah   s   new string s ToCharArray   Reverse   ToArray

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public static string Reverse string input        return string Concat Enumerable Reverse input        Of course you can extend string class with Reverse method  public static class StringExtensions       public static string Reverse this string input                return string Concat Enumerable Reverse input

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If you want to play a really dangerous game  then this is by far the fastest way there is  around four times faster than the Array Reverse method   It s an in-place reverse using pointers   Note that I really do not recommend this for any use  ever  have a look here for some reasons why you should not use this method   but it s just interesting to see that it can be done  and that strings aren t really immutable once you turn on unsafe code   public static unsafe string Reverse string text        if  string IsNullOrEmpty text                 return text             fixed  char  pText   text                char  pStart   pText          char  pEnd   pText   text Length - 1          for  int i   text Length   2  i  gt   0  i--                        char temp    pStart               pStart      pEnd               pEnd--   temp                     return text

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Try using Array Reverse   public string Reverse string str        char   array   str ToCharArray        Array Reverse array       return new string array

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Starting with  NET Core 2 1 there is a new way to reverse a string using the string Create method   Note that this solution does not handle Unicode combining characters etc  correctly  as  Les Mise u0301rables  would be converted to  selbar  siM seL   The the other answers for a better solution   public static string Reverse string input        return string Create lt string gt  input Length  input   chars  state    gt                state AsSpan   CopyTo chars           chars Reverse                This essentially copies the characters of input to a new string and reverses the new string in-place   Why is string Create useful   When we create a string from an existing array  a new internal array is allocated and the values are copied  Otherwise  it would be possible to mutate a string after its creation  in a safe environment   That is  in the following snippet we have to allocate an array of length 10 twice  one as the buffer and one as the string s internal array   var chars   new char 10      set array values var str   new string chars     string Create essentially allows us to manipulate the internal array during creation time of the string  This is  we do not need a buffer anymore and can therefore avoid allocating that one char array   Steve Gordon has written about it in more detail here  There is also an article on MSDN   How to use string Create   public static string Create lt TState gt  int length  TState state  SpanAction lt char  TState gt  action     The method takes three parameters    The length of the string to create  the data you want to use to dynamically create the new string  and a delegate that creates the final string from the data  where the first parameter points to the internal char array of the new string and the second is the data  state  you passed to string Create    Inside the delegate we can specify how the new string is created from the data  In our case  we just copy the characters of the input string to the Span used by the new string  Then we reverse the Span and hence the whole string is reversed   Benchmarks  To compare my proposed way of reversing a string with the accepted answer  I have written two benchmarks using BenchmarkDotNet   public class StringExtensions       public static string ReverseWithArray string input                var charArray   input ToCharArray            Array Reverse charArray           return new string charArray              public static string ReverseWithStringCreate string input                return string Create input Length  input   chars  state    gt                        state AsSpan   CopyTo chars               chars Reverse                          MemoryDiagnoser  public class StringReverseBenchmarks       private string input        Params 10  100  1000       public int InputLength   get  set           GlobalSetup      public void SetInput                    Creates a random string of the given length         this input   RandomStringGenerator GetString InputLength               Benchmark Baseline   true       public string WithReverseArray     gt  StringExtensions ReverseWithArray input         Benchmark      public string WithStringCreate     gt  StringExtensions ReverseWithStringCreate input       Here are the results on my machine     Method             InputLength           Mean        Error      StdDev    Gen 0   Allocated     ----------------   -----------   -----------    ---------    --------    -----    --------      WithReverseArray   10               45 464 ns    0 4836 ns   0 4524 ns   0 0610        96 B     WithStringCreate   10               39 749 ns    0 3206 ns   0 2842 ns   0 0305        48 B                                                                                                     WithReverseArray   100             175 162 ns    2 8766 ns   2 2458 ns   0 2897       456 B     WithStringCreate   100             125 284 ns    2 4657 ns   2 0590 ns   0 1473       232 B                                                                                                     WithReverseArray   1000          1 523 544 ns    9 8808 ns   8 7591 ns   2 5768      4056 B     WithStringCreate   1000          1 078 957 ns   10 2948 ns   9 6298 ns   1 2894      2032 B     As you can see  with ReverseWithStringCreate we allocate only half of the memory used by the ReverseWithArray method

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Using LINQ s Aggregate function  string s    Karthik U   s   s Aggregate new StringBuilder     o  p    gt  o Insert 0  p   ToString

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I ve made a C  port from Microsoft VisualBasic Strings  I m not sure why they keep such useful functions  from VB  outside the System String in Framework  but still under Microsoft VisualBasic  Same scenario for financial functions  e g  Microsoft VisualBasic Financial Pmt      public static string StrReverse this string expression        if   expression    null           return          int srcIndex       var length   expression Length      if  length    0          return            CONSIDER  Get System String to add a surrogate aware Reverse method        Detect if there are any graphemes that need special handling     for  srcIndex   0  srcIndex  lt   length - 1  srcIndex                  var ch   expression srcIndex           var uc   char GetUnicodeCategory ch           if  uc    UnicodeCategory Surrogate    uc    UnicodeCategory NonSpacingMark    uc    UnicodeCategory SpacingCombiningMark    uc    UnicodeCategory EnclosingMark                          Need to use special handling             return InternalStrReverse expression  srcIndex  length                        var chars   expression ToCharArray        Array Reverse chars       return new string chars          lt remarks gt This routine handles reversing Strings containing graphemes     GRAPHEME  a text element that is displayed as a single character lt  remarks gt  private static string InternalStrReverse string expression  int srcIndex  int length          This code can only be hit one time     var sb   new StringBuilder length    Length   length         var textEnum   StringInfo GetTextElementEnumerator expression  srcIndex          Init enumerator position     if   textEnum MoveNext                  return                var lastSrcIndex   0      var destIndex   length - 1         Copy up the first surrogate found     while  lastSrcIndex  lt  srcIndex                sb destIndex    expression lastSrcIndex           destIndex -  1          lastSrcIndex    1               Now iterate through the text elements and copy them to the reversed string     var nextSrcIndex   textEnum ElementIndex       while  destIndex  gt   0                srcIndex   nextSrcIndex             Move to next element         nextSrcIndex    textEnum MoveNext      textEnum ElementIndex   length          lastSrcIndex   nextSrcIndex - 1           while  lastSrcIndex  gt   srcIndex                        sb destIndex    expression lastSrcIndex               destIndex -  1              lastSrcIndex -  1                       return sb ToString

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public static string Reverse2 string x                        char   charArray   new char x Length               int len   x Length - 1              for  int i   0  i  lt   len  i                    charArray i    x len - i               return new string charArray

[c#] Best way to reverse a string

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