Identify if a string is a number

Question

If I have these strings     abc      false  123     true  ab2     false   Is there a command  like IsNumeric   or something else  that can identify if a string is a valid number

User · Answer

If you want to know if a string is a number, you could always try parsing it:

var numberString = "123";
int number;

int.TryParse(numberString , out number);

Note that TryParse returns a bool, which you can use to check if your parsing succeeded.

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This will return true if input is all numbers  Don t know if it s any better than TryParse  but it will work   Regex IsMatch input      d       If you just want to know if it has one or more numbers mixed in with characters  leave off the     and     Regex IsMatch input     d     Edit  Actually I think it is better than TryParse because a very long string could potentially overflow TryParse

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Pull in a reference to Visual Basic in your project and use its Information IsNumeric method such as shown below and be able to capture floats as well as integers unlike the answer above which only catches ints          Using Microsoft VisualBasic       var txt    ABCDEFG        if  Information IsNumeric txt           Console WriteLine   Numeric     IsNumeric  12 3       true IsNumeric  1       true IsNumeric  abc       false

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With c  7 it you can inline the out variable   if int TryParse str  out int v

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I guess this answer will just be lost in between all the other ones  but anyway  here goes   I ended up on this question via Google because I wanted to check if a string was numeric so that I could just use double Parse  123   instead of the TryParse   method   Why  Because it s annoying to have to declare an out variable and check the result of TryParse   before you know if the parse failed or not  I want to use the ternary operator to check if the string is numerical and then just parse it in the first ternary expression or provide a default value in the second ternary expression   Like this   var doubleValue   IsNumeric numberAsString    double Parse numberAsString    0    It s just a lot cleaner than   var doubleValue   0  if  double TryParse numberAsString  out doubleValue           whatever you want to do with doubleValue     I made a couple extension methods for these cases     Extension method one  public static bool IsParseableAs lt TInput gt  this string value        var type   typeof TInput        var tryParseMethod   type GetMethod  TryParse   BindingFlags Static   BindingFlags Public  Type DefaultBinder          new     typeof string   type MakeByRefType      null       if  tryParseMethod    null  return false       var arguments   new     value  Activator CreateInstance type         return  bool  tryParseMethod Invoke null  arguments       Example    123  IsParseableAs lt double gt      double Parse sNumber    0    Because IsParseableAs   tries to parse the string as the appropriate type instead of just checking if the string is  numeric  it should be pretty safe  And you can even use it for non numeric types that have a TryParse   method  like DateTime   The method uses reflection and you end up calling the TryParse   method twice which  of course  isn t as efficient  but not everything has to be fully optimized  sometimes convenience is just more important   This method can also be used to easily parse a list of numeric strings into a list of double or some other type with a default value without having to catch any exceptions   var sNumbers   new     10    20    30    var dValues   sNumbers Select s   gt  s IsParseableAs lt double gt      double Parse s    0       Extension method two  public static TOutput ParseAs lt TOutput gt  this string value  TOutput defaultValue        var type   typeof TOutput        var tryParseMethod   type GetMethod  TryParse   BindingFlags Static   BindingFlags Public  Type DefaultBinder          new     typeof string   type MakeByRefType      null       if  tryParseMethod    null  return defaultValue       var arguments   new object     value  null        return   bool  tryParseMethod Invoke null  arguments      TOutput  arguments 1    defaultValue      This extension method lets you parse a string as any type that has a TryParse   method and it also lets you specify a default value to return if the conversion fails   This is better than using the ternary operator with the extension method above as it only does the conversion once   It still uses reflection though     Examples    123  ParseAs lt int gt  10    abc  ParseAs lt int gt  25    123 78  ParseAs lt double gt  10    abc  ParseAs lt double gt  107 4    2014-10-28  ParseAs lt DateTime gt  DateTime MinValue    monday  ParseAs lt DateTime gt  DateTime MinValue     Outputs   123 25 123 78 107 4 28 10 2014 00 00 00 01 01 0001 00 00 00

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Use these extension methods to clearly distinguish between a check if the string is numerical and if the string only contains 0-9 digits  public static class ExtensionMethods            lt summary gt          Returns true if string could represent a valid number  including decimals and local culture symbols          lt  summary gt      public static bool IsNumeric this string s                decimal d          return decimal TryParse s  System Globalization NumberStyles Any  System Globalization CultureInfo CurrentCulture  out d                   lt summary gt          Returns true only if string is wholy comprised of numerical digits          lt  summary gt      public static bool IsNumbersOnly this string s                if  s    null    s    string Empty              return false           foreach  char c in s                        if  c  lt   0     c  gt   9      Avoid using  IsDigit or  IsNumeric as they will return true for other characters                 return false                     return true

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The best flexible solution with  net built-in function called- char IsDigit  It works with unlimited long numbers  It will only return true if each character is a numeric number  I used it lot of times with no issues and much easily cleaner solution I ever found  I made a example method Its ready to use  In addition I added validation for null and empty input  So the method is now totally bulletproof  public static bool IsNumeric string strNumber                if  string IsNullOrEmpty strNumber                         return false                    else                       int numberOfChar   strNumber Count                if  numberOfChar  gt  0                                bool r   strNumber All char IsDigit                   return r                            else                               return false

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In case you don t want to use int Parse or double Parse  you can roll your own with something like this   public static class Extensions       public static bool IsNumeric this string s                foreach  char c in s                        if   char IsDigit c   amp  amp  c                                       return false                                   return true

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Double TryParse  bool Double TryParse string s  out double result

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public static bool IsNumeric this string input        int n      if   string IsNullOrEmpty input      Replace     null  Replace     null                foreach  var i in input                        if   int TryParse i ToString    out n                                 return false                                   return true            return false

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This is probably the best option in C    If you want to know if the string contains a whole number  integer    string someString         int myInt  bool isNumerical   int TryParse someString  out myInt     The TryParse method will try to convert the string to a number  integer  and if it succeeds it will return true and place the corresponding number in myInt  If it can t  it returns false   Solutions using the int Parse someString  alternative shown in other responses works  but it is much slower because throwing exceptions is very expensive  TryParse      was added to the C  language in version 2  and until then you didn t have a choice  Now you do  you should therefore avoid the Parse   alternative   If you want to accept decimal numbers  the decimal class also has a  TryParse      method  Replace int with decimal in the above discussion  and the same principles apply

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Hope this helps  string myString    abc   double num  bool isNumber   double TryParse myString   out num    if isNumber      string is number   else     string is not a number

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Here is the C  method  Int TryParse Method  String  Int32

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int n  bool isNumeric   int TryParse  123   out n     Update As of C  7   var isNumeric   int TryParse  123   out int n     or if you don t need the number you can discard the out parameter  var isNumeric   int TryParse  123   out       The var s can be replaced by their respective types

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To my knowledge I did this in a simple way static void Main string   args        string a  b      int f1  f2  x  y      Console WriteLine  Enter two inputs        a   Convert ToString Console ReadLine         b   Console ReadLine        f1   find a       f2   find b        if  f1    0  amp  amp  f2    0                x   Convert ToInt32 a           y   Convert ToInt32 b           Console WriteLine  Two inputs r number  n so that addition of these text box is       x   y  ToString               else         Console WriteLine  One or two inputs r string  n so that concatenation of these text box is        a   b        Console ReadKey       static int find string s        string s1           int f      for  int i   0  i  lt  s Length  i           for  int j   0  j  lt   9  j                        string c   j ToString               if  c 0     s i                               s1    c 0                              if  s    s1          f   0      else         f   1       return f

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Try the reges below  new Regex     d 4    IsMatch  6         false new Regex     d 4    IsMatch  68ab      false new Regex     d 4    IsMatch  1111abcdefg   new Regex     d    IsMatch  6      true  any length but at least one digit

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You can always use the built in TryParse methods for many datatypes to see if the string in question will pass    Example   decimal myDec  var Result   decimal TryParse  123   out myDec     Result would then   True  decimal myDec  var Result   decimal TryParse  abc   out myDec     Result would then   False

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You can use TryParse to determine if the string can be parsed into an integer   int i  bool bNum   int TryParse str  out i     The boolean will tell you if it worked or not

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If you want to check if a string is a number  I m assuming it s a string since if it s a number  duh  you know it s one     Without regex and using Microsoft s code as much as possible   you could also do   public static bool IsNumber this string aNumber         BigInteger temp big int       var is number   BigInteger TryParse aNumber  out temp big int        return is number      This will take care of the usual nasties    Minus  -  or Plus     in the beginning contains decimal character BigIntegers won t parse numbers with decimal points   So  BigInteger Parse  3 3   will throw an exception  and TryParse for the same will return false  no funny non-digits covers cases where the number is bigger than the usual use of Double TryParse   You ll have to add a reference to System Numerics and have  using System Numerics  on top of your class  well  the second is a bonus I guess

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UPDATE of Kunal Noel Answer  stringTest All char IsDigit      This returns true if all characters of the string are digits    But  for this case we have that empty strings will pass that test  so  you can   if   string IsNullOrEmpty stringTest   amp  amp  stringTest All char IsDigit          Do your logic here

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You can also use   stringTest All char IsDigit     It will return true for all Numeric Digits  not float  and false if input string is any sort of alphanumeric   Please note  stringTest should not be an empty string as this would pass the test of being numeric

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If you want to catch a broader spectrum of numbers     la PHP s is numeric  you can use the following      From PHP documentation for is numeric     http   php net manual en function is-numeric php      Finds whether the given variable is numeric      Numeric strings consist of optional sign  any number of digits  optional decimal part and optional    exponential part  Thus  0123 45e6 is a valid numeric value      Hexadecimal  e g  0xf4c3b00c   Binary  e g  0b10100111001   Octal  e g  0777  notation is allowed too but    only without sign  decimal and exponential part  static readonly Regex  isNumericRegex       new Regex                            Hex     0x 0-9a-f                               Bin     0b 01                                    Oct     0 0-7                                   Dec         0   -      0       d      d  e d                                static bool IsNumeric  string value         return  isNumericRegex IsMatch  value        Unit Test   static void IsNumericTest         string   l unitTests   new string               123           TRUE             abc           FALSE             12 3          TRUE              12 3         TRUE             -12 3         TRUE             1 23e2        TRUE             -1e23         TRUE             1 2ef         FALSE             0x0           TRUE             0xfff         TRUE             0xf1f         TRUE             0xf1g         FALSE             0123          TRUE             0999          FALSE  not octal               0999         TRUE  forced decimal              0b0101        TRUE             0b0102        FALSE                foreach   string l unitTest in l unitTests           Console WriteLine  l unitTest       gt      IsNumeric  l unitTest   ToString           Console ReadKey  true        Keep in mind that just because a value is numeric doesn t mean it can be converted to a numeric type  For example   999999999999999999999999999999 9999999999  is a perfeclty valid numeric value  but it won t fit into a  NET numeric type  not one defined in the standard library  that is

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I ve used this function several times   public static bool IsNumeric object Expression        double retNum       bool isNum   Double TryParse Convert ToString Expression   System Globalization NumberStyles Any  System Globalization NumberFormatInfo InvariantInfo  out retNum       return isNum      But you can also use   bool b1   Microsoft VisualBasic Information IsNumeric  1      true bool b2   Microsoft VisualBasic Information IsNumeric  1aa       false   From Benchmarking IsNumeric Options    source  aspalliance com       source  aspalliance com

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I know this is an old thread  but none of the answers really did it for me - either inefficient  or not encapsulated for easy reuse  I also wanted to ensure it returned false if the string was empty or null  TryParse returns true in this case  an empty string does not cause an error when parsing as a number   So  here s my string extension method   public static class Extensions            lt summary gt          Returns true if string is numeric and not empty or null or whitespace          Determines if string is numeric by parsing as Double          lt  summary gt           lt param name  str  gt  lt  param gt           lt param name  style  gt Optional style - defaults to NumberStyles Number  leading and trailing whitespace  leading and trailing sign  decimal point and thousands separator   lt  param gt           lt param name  culture  gt Optional CultureInfo - defaults to InvariantCulture lt  param gt           lt returns gt  lt  returns gt      public static bool IsNumeric this string str  NumberStyles style   NumberStyles Number          CultureInfo culture   null                double num          if  culture    null  culture   CultureInfo InvariantCulture          return Double TryParse str  style  culture  out num   amp  amp   String IsNullOrWhiteSpace str             Simple to use   var mystring    1234 56789   var test   mystring IsNumeric      Or  if you want to test other types of number  you can specify the  style   So  to convert a number with an Exponent  you could use   var mystring    5 2453232E6   var test   mystring IsNumeric style  NumberStyles AllowExponent     Or to test a potential Hex string  you could use   var mystring    0xF67AB2   var test   mystring IsNumeric style  NumberStyles HexNumber    The optional  culture  parameter can be used in much the same way   It is limited by not being able to convert strings that are too big to be contained in a double  but that is a limited requirement and I think if you are working with numbers larger than this  then you ll probably need additional specialised number handling functions anyway

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All the Answers are Useful  But while searching for a solution where the Numeric value is 12 digits or more  in my case   then while debugging  I found the following solution useful    double tempInt   0  bool result   double TryParse  Your 12 Digit Or more StringValue   out tempInt     Th result variable will give you true or false

[c#] Identify if a string is a number

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