How can I get a count of the total number of digits in a number

Question

How can I get a count of the total number of digits of a number in C   For example  the number 887979789 has 9 digits

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Create a method that returns all digits  and another that counts them   public static int GetNumberOfDigits this long value        return value GetDigits   Count       public static IEnumerable lt int gt  GetDigits this long value        do               yield return  int  value   10           value    10        while  value    0       This felt like the more intuitive approach to me when tackling this problem  I tried the Log10 method first due to its apparent simplicity  but it has an insane amount of corner cases and precision problems   I also found the if-chain proposed in the other answer to a bit ugly to look at   I know this is not the most efficient method  but it gives you the other extension to return the digits as well for other uses  you can just mark it private if you don t need to use it outside the class    Keep in mind that it does not consider the negative sign as a digit

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Here s an implementation using a binary search  Looks to be the fastest so far on int32   Int64 implementation is left as an exercise for the reader     I tried using Array BinarySearch rather than hard-coding the tree  but that was about half the speed   EDIT  A lookup table is much faster than the binary search  at the expense of using more memory  Realistically I d probably use the binary search one in production  the lookup table is a lot of complexity for a speed gain that s likely to be overshadowed by other parts of the software   Lookup-Table  439 ms Binary-Search  1069 ms If-Chain  1409 ms Log10  1145 ms While  1768 ms String  5153 ms   Lookup table version   static byte    0000llll   new byte 0x10000   static byte    FFFFllll   new byte 0x10001   static sbyte    hhhhXXXXdigits   new sbyte 0x10000       Special cases where the high DWORD is not enough information to find out how    many digits  static ushort    lowordSplits   new ushort 12   static sbyte    lowordSplitDigitsLT   new sbyte 12   static sbyte    lowordSplitDigitsGE   new sbyte 12    static Int32Extensions            Simple lookup tables for number of digits where value is            0000xxxx  0    65535         or FFFFxxxx  -1    -65536      precomputePositiveLo16        precomputeNegativeLo16            Hiword is a little more complex     precomputeHiwordDigits       private static void precomputeHiwordDigits         int b   0       for int hhhh   0  hhhh  lt   0xFFFF  hhhh                     For hiword hhhh  calculate integer value for loword of 0000 and FFFF          int hhhh0000    unchecked hhhh   0x10000        wrap around on negatives         int hhhhFFFF   hhhh0000   0xFFFF              How many decimal digits for each          int digits0000   hhhh0000 Digits IfChain            int digitsFFFF   hhhhFFFF Digits IfChain                If same number of decimal digits  we know that when we see that hiword            we don t have to look at the loword to know the right answer          if digits0000    digitsFFFF                         hhhhXXXXdigits hhhh     sbyte digits0000                    else                       bool negative   hhhh  gt   0x8000                  Calculate 10  100  1000  10000 etc             int tenToThePower    int Math Pow 10   negative   digits0000   digitsFFFF  - 1                   Calculate the loword of the 10 n value              ushort lowordSplit   unchecked  ushort tenToThePower               if negative                  lowordSplit   unchecked  ushort  2    ushort  lowordSplit                    Store the split point and digits into these arrays              lowordSplits b    lowordSplit               lowordSplitDigitsLT b     sbyte digits0000               lowordSplitDigitsGE b     sbyte digitsFFFF                  Store the minus of the array index into the digits lookup  We look for                minus values and use these to trigger using the split points logic               hhhhXXXXdigits hhhh     sbyte  -b               b                       private static void precomputePositiveLo16         for int i   0  i  lt   9  i             0000llll i    1       for int i   10  i  lt   99  i             0000llll i    2       for int i   100  i  lt   999  i             0000llll i    3       for int i   1000  i  lt   9999  i             0000llll i    4       for int i   10000  i  lt   65535  i             0000llll i    5     private static void precomputeNegativeLo16         for int i   0  i  lt   9  i             FFFFllll 65536 - i    1       for int i   10  i  lt   99  i             FFFFllll 65536 - i    2       for int i   100  i  lt   999  i             FFFFllll 65536 - i    3       for int i   1000  i  lt   9999  i             FFFFllll 65536 - i    4       for int i   10000  i  lt   65535  i             FFFFllll 65536 - i    5       public static int Digits LookupTable this int n           Split input into low word and high word      ushort l   unchecked  ushort n       ushort h   unchecked  ushort  n  gt  gt  16            If the hiword is 0000 or FFFF we have precomputed tables for these      if h    0x0000                return  0000llll l             else if h    0xFFFF                return  FFFFllll l                 In most cases the hiword will tell us the number of decimal digits      sbyte digits    hhhhXXXXdigits h           We put a positive number in this lookup table when        hhhh0000    hhhhFFFF all have the same number of decimal digits      if digits  gt  0          return digits          Where the answer is different for hhhh0000 to hhhhFFFF  we need to        look up in a separate array to tell us at what loword the change occurs      var splitIndex    sbyte  -digits        ushort lowordSplit    lowordSplits splitIndex           Pick the correct answer from the relevant array  depending whether        our loword is lower than the split point or greater equal  Note that for        negative numbers  the loword is LOWER for MORE decimal digits      if l  lt  lowordSplit          return  lowordSplitDigitsLT splitIndex       else         return  lowordSplitDigitsGE splitIndex       Binary search version          public static int Digits BinarySearch this int n                        if n  gt   0                                if n  lt   9999     0    9999                                       if n  lt   99     0    99                                               return  n  lt   9    1   2                                            else    100    9999                                               return  n  lt   999    3   4                                                          else    10000    int MaxValue                                       if n  lt   9 999 999     10000    9 999 999                                               if n  lt   99 999                              return 5                          else if n  lt   999 999                              return 6                          else                             return 7                                            else    10 000 000    int MaxValue                                               if n  lt   99 999 999                              return 8                          else if n  lt   999 999 999                              return 9                          else                             return 10                                                                    else                               if n  gt   -9999     -9999    -1                                       if n  gt   -99     -99    -1                                               return  n  gt   -9    1   2                                            else    -9999    -100                                               return  n  gt   -999    3   4                                                          else    int MinValue    -10000                                       if n  gt   -9 999 999     -9 999 999    -10000                                               if n  gt   -99 999                              return 5                          else if n  gt   -999 999                              return 6                          else                             return 7                                            else    int MinValue    -10 000 000                                                if n  gt   -99 999 999                              return 8                          else if n  gt   -999 999 999                              return 9                          else                             return 10                                                                           Stopwatch sw0   new Stopwatch            sw0 Start            for int i   0  i  lt  size    i  samples i  Digits BinarySearch            sw0 Stop            Console WriteLine   Binary-Search   sw0 ElapsedMilliseconds  ms

User · Answer

static void Main string   args        long blah   20948230498204      Console WriteLine blah ToString   Length

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Without converting to a string you could try   Math Ceiling Math Log10 n      Correction following ysap s comment   Math Floor Math Log10 n    1

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It depends what exactly you want to do with the digits  You can iterate through the digits starting from the last to the first one like this   int tmp   number  int lastDigit   0  do       lastDigit   tmp   10      doSomethingWithDigit lastDigit       tmp    10    while  tmp    0

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convert into string and then you can count tatal no of digit by  length method  Like   String numberString    855865264  toString    int NumLen   numberString  Length

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Answers already here work for unsigned integers  but I have not found good solutions for getting number of digits from decimals and doubles   public static int Length double number        number   Math Abs number       int length   1      while   number    10   gt   1          length        return length      number of digits in 0   1    number of digits in 22 1   2    number of digits in -23   2   You may change input type from double to decimal if precision matters  but decimal has a limit too

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Try This      myint ToString   Length   Does that work

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The answer of Steve is correct  but it doesn t work for integers less than 1   Here an updated version that does work for negatives   int digits   n    0   1   Math Floor Math Log10 Math Abs n     1

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int i   855865264  int NumLen   i ToString   Length

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Using recursion  sometimes asked on interviews   public int CountDigits int number           In case of negative numbers     number   Math Abs number        if  number  gt   10          return CountDigits number   10    1      return 1

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Not directly C   but the formula is  n   floor log10 x  1

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The Solution  Any of the following extension methods will do the job  All of them consider the minus sign as a digit  and work correctly for all possible input values  They also work for  NET Framework and for  NET Core  There are however relevant performance differences  discussed below   depending on your choice of Platform   Framework   Int32 version   public static class Int32Extensions          IF-CHAIN      public static int Digits IfChain this int n                if  n  gt   0                        if  n  lt  10  return 1              if  n  lt  100  return 2              if  n  lt  1000  return 3              if  n  lt  10000  return 4              if  n  lt  100000  return 5              if  n  lt  1000000  return 6              if  n  lt  10000000  return 7              if  n  lt  100000000  return 8              if  n  lt  1000000000  return 9              return 10                    else                       if  n  gt  -10  return 2              if  n  gt  -100  return 3              if  n  gt  -1000  return 4              if  n  gt  -10000  return 5              if  n  gt  -100000  return 6              if  n  gt  -1000000  return 7              if  n  gt  -10000000  return 8              if  n  gt  -100000000  return 9              if  n  gt  -1000000000  return 10              return 11                          USING LOG10      public static int Digits Log10 this int n    gt          n    0   1    n  gt  0   1   2     int Math Log10 Math Abs  double n            WHILE LOOP      public static int Digits While this int n                int digits   n  lt  0   2   1          while   n    10     0    digits          return digits                STRING CONVERSION      public static int Digits String this int n    gt          n ToString   Length      Int64 version   public static class Int64Extensions          IF-CHAIN      public static int Digits IfChain this long n                if  n  gt   0                        if  n  lt  10L  return 1              if  n  lt  100L  return 2              if  n  lt  1000L  return 3              if  n  lt  10000L  return 4              if  n  lt  100000L  return 5              if  n  lt  1000000L  return 6              if  n  lt  10000000L  return 7              if  n  lt  100000000L  return 8              if  n  lt  1000000000L  return 9              if  n  lt  10000000000L  return 10              if  n  lt  100000000000L  return 11              if  n  lt  1000000000000L  return 12              if  n  lt  10000000000000L  return 13              if  n  lt  100000000000000L  return 14              if  n  lt  1000000000000000L  return 15              if  n  lt  10000000000000000L  return 16              if  n  lt  100000000000000000L  return 17              if  n  lt  1000000000000000000L  return 18              return 19                    else                       if  n  gt  -10L  return 2              if  n  gt  -100L  return 3              if  n  gt  -1000L  return 4              if  n  gt  -10000L  return 5              if  n  gt  -100000L  return 6              if  n  gt  -1000000L  return 7              if  n  gt  -10000000L  return 8              if  n  gt  -100000000L  return 9              if  n  gt  -1000000000L  return 10              if  n  gt  -10000000000L  return 11              if  n  gt  -100000000000L  return 12              if  n  gt  -1000000000000L  return 13              if  n  gt  -10000000000000L  return 14              if  n  gt  -100000000000000L  return 15              if  n  gt  -1000000000000000L  return 16              if  n  gt  -10000000000000000L  return 17              if  n  gt  -100000000000000000L  return 18              if  n  gt  -1000000000000000000L  return 19              return 20                          USING LOG10      public static int Digits Log10 this long n    gt          n    0L   1    n  gt  0L   1   2     int Math Log10 Math Abs  double n            WHILE LOOP      public static int Digits While this long n                int digits   n  lt  0   2   1          while   n    10L     0L    digits          return digits                STRING CONVERSION      public static int Digits String this long n    gt          n ToString   Length      Discussion  This answer includes tests performed for both Int32 and Int64 types  using an array of 100 000 000 randomly sampled int   long numbers  The random dataset is pre-processed into an array before executing the tests   Consistency tests among the 4 different methods were also executed  for MinValue  negative border cases  -1  0  1  positive border cases  MaxValue  and also for the whole random dataset  No consistency tests fail for the above provided methods  EXCEPT for the LOG10 method  this is discussed later    The tests were executed on  NET Framework 4 7 2 and  NET Core 2 2  for x86 and x64 platforms  on a 64-bit Intel Processor machine  with Windows 10  and with VS2017 v 15 9 17  The following 4 cases have the same effect on performance results    NET Framework  x86    Platform   x86 Platform   AnyCPU  Prefer 32-bit is checked in project settings    NET Framework  x64    Platform   x64 Platform   AnyCPU  Prefer 32-bit is unchecked in project settings    NET Core  x86     C  Program Files  x86  dotnet dotnet exe  bin Release netcoreapp2 2 ConsoleApp dll  C  Program Files  x86  dotnet dotnet exe  bin x86 Release netcoreapp2 2 ConsoleApp dll    NET Core  x64     C  Program Files dotnet dotnet exe  bin Release netcoreapp2 2 ConsoleApp dll  C  Program Files dotnet dotnet exe  bin x64 Release netcoreapp2 2 ConsoleApp dll   Results  The performance tests below produce a uniform distribution of values among the wide range of values an integer could assume  This means there is a much higher chance of testing values with a big count of digits  In real life scenarios  most values may be small  so the IF-CHAIN should perform even better  Furthermore  the processor will cache and optimize the IF-CHAIN decisions according to your dataset   As  AlanSingfield pointed out in the comment section  the LOG10 method had to be fixed with a casting to double inside Math Abs   for the case when the input value is int MinValue or long MinValue   Regarding the early performance tests I ve implemented before editing this question  it had to be edited a million times already   there was a specific case pointed out by  Gy  rgyKoszeg  in which the IF-CHAIN method performs slower than the LOG10 method   This still happens  although the magnitude of the difference became much lower after the fix for the issue pointed out by  AlanSingfield  This fix  adding a cast to double  causes a computation error when the input value is exactly -999999999999999999  the LOG10 method returns 20 instead of 19  The LOG10 method also must have a if guard for the case when the input value is zero   The LOG10 method is quite tricky to get working for all values  which means you should avoid it  If someone finds a way to make it work correctly for all the consistency tests below  please post a comment   The WHILE method also got a recent refactored version which is faster  but it is still slow for Platform   x86  I could not find the reason why  until now    The STRING method is consistently slow  it greedily allocates too much memory for nothing  Interestingly  in  NET Core  string allocation seems to be much faster than in  NET Framework  Good to know   The IF-CHAIN method should outperform all other methods in 99 99  of the cases  and  in my personal opinion  is your best choice  considering all the adjusts necessary to make the LOG10 method work correctly  and the bad performance of the other two methods    Finally  the results are     Since these results are hardware-dependent  I recommend anyway running the performance tests below on your own computer if you really need to be 100  sure in your specific case   Test Code  Below is the code for the performance test  and the consistency test too  The same code is used for both  NET Framework and  NET Core   using System  using System Diagnostics   namespace NumberOfDigits          Performance Tests      class Program               private static void Main string   args                        Console WriteLine   r n NET Core                 RunTests Int32                RunTests Int64                          Int32 Performance Tests          private static void RunTests Int32                         Console WriteLine   r nInt32                 const int size   100000000              int   samples   new int size               Random random   new Random  int DateTime Now Ticks               for  int i   0  i  lt  size    i                  samples i    random Next int MinValue  int MaxValue                Stopwatch sw1   new Stopwatch                sw1 Start                for  int i   0  i  lt  size    i  samples i  Digits IfChain                sw1 Stop                Console WriteLine   IfChain   sw1 ElapsedMilliseconds  ms                 Stopwatch sw2   new Stopwatch                sw2 Start                for  int i   0  i  lt  size    i  samples i  Digits Log10                sw2 Stop                Console WriteLine   Log10   sw2 ElapsedMilliseconds  ms                 Stopwatch sw3   new Stopwatch                sw3 Start                for  int i   0  i  lt  size    i  samples i  Digits While                sw3 Stop                Console WriteLine   While   sw3 ElapsedMilliseconds  ms                 Stopwatch sw4   new Stopwatch                sw4 Start                for  int i   0  i  lt  size    i  samples i  Digits String                sw4 Stop                Console WriteLine   String   sw4 ElapsedMilliseconds  ms                     Start of consistency tests              Console WriteLine  Running consistency tests                   bool isConsistent   true                  Consistency test on random set              for  int i   0  i  lt  samples Length    i                                int s   samples i                   int a   s Digits IfChain                    int b   s Digits Log10                    int c   s Digits While                    int d   s Digits String                    if  a    b    c    d    a    c                                        Console WriteLine   Digits  s    IfChain  a  Log10  b  While  c  String  d                         isConsistent   false                      break                                                  Consistency test of special values              samples   new int                                 0                  int MinValue  -1000000000  -999999999  -100000000  -99999999  -10000000  -9999999  -1000000  -999999  -100000  -99999  -10000  -9999  -1000  -999  -100  -99  -10  -9  - 1                  int MaxValue  1000000000  999999999  100000000  99999999  10000000  9999999  1000000  999999  100000  99999  10000  9999  1000  999  100  99  10  9   1                             for  int i   0  i  lt  samples Length    i                                int s   samples i                   int a   s Digits IfChain                    int b   s Digits Log10                    int c   s Digits While                    int d   s Digits String                    if  a    b    c    d    a    c                                        Console WriteLine   Digits  s    IfChain  a  Log10  b  While  c  String  d                         isConsistent   false                      break                                                  Consistency test result              if  isConsistent                  Console WriteLine  Consistency tests are OK                          Int64 Performance Tests          private static void RunTests Int64                         Console WriteLine   r nInt64                 const int size   100000000              long   samples   new long size               Random random   new Random  int DateTime Now Ticks               for  int i   0  i  lt  size    i                  samples i    Math Sign random Next -1  1      long  random NextDouble     long MaxValue                Stopwatch sw1   new Stopwatch                sw1 Start                for  int i   0  i  lt  size    i  samples i  Digits IfChain                sw1 Stop                Console WriteLine   IfChain   sw1 ElapsedMilliseconds  ms                 Stopwatch sw2   new Stopwatch                sw2 Start                for  int i   0  i  lt  size    i  samples i  Digits Log10                sw2 Stop                Console WriteLine   Log10   sw2 ElapsedMilliseconds  ms                 Stopwatch sw3   new Stopwatch                sw3 Start                for  int i   0  i  lt  size    i  samples i  Digits While                sw3 Stop                Console WriteLine   While   sw3 ElapsedMilliseconds  ms                 Stopwatch sw4   new Stopwatch                sw4 Start                for  int i   0  i  lt  size    i  samples i  Digits String                sw4 Stop                Console WriteLine   String   sw4 ElapsedMilliseconds  ms                    Start of consistency tests              Console WriteLine  Running consistency tests                   bool isConsistent   true                  Consistency test on random set              for  int i   0  i  lt  samples Length    i                                long s   samples i                   int a   s Digits IfChain                    int b   s Digits Log10                    int c   s Digits While                    int d   s Digits String                    if  a    b    c    d    a    c                                        Console WriteLine   Digits  s    IfChain  a  Log10  b  While  c  String  d                         isConsistent   false                      break                                                  Consistency test of special values              samples   new long                                  0                  long MinValue  -1000000000000000000  -999999999999999999  -100000000000000000  -99999999999999999  -10000000000000000  -9999999999999999  -1000000000000000  -999999999999999  -100000000000000  -99999999999999  -10000000000000  -9999999999999  -1000000000000  -999999999999  -100000000000  -99999999999  -10000000000  -9999999999  -1000000000  -999999999  -100000000  -99999999  -10000000  -9999999  -1000000  -999999  -100000  -99999  -10000  -9999  -1000  -999  -100  -99  -10  -9  - 1                  long MaxValue  1000000000000000000  999999999999999999  100000000000000000  99999999999999999  10000000000000000  9999999999999999  1000000000000000  999999999999999  100000000000000  99999999999999  10000000000000  9999999999999  1000000000000  999999999999  100000000000  99999999999  10000000000  9999999999  1000000000  999999999  100000000  99999999  10000000  9999999  1000000  999999  100000  99999  10000  9999  1000  999  100  99  10  9   1                             for  int i   0  i  lt  samples Length    i                                long s   samples i                   int a   s Digits IfChain                    int b   s Digits Log10                    int c   s Digits While                    int d   s Digits String                    if  a    b    c    d    a    c                                        Console WriteLine   Digits  s    IfChain  a  Log10  b  While  c  String  d                         isConsistent   false                      break                                                  Consistency test result              if  isConsistent                  Console WriteLine  Consistency tests are OK

User · Answer

dividing a number by 10 will give you the left most digit then doing a mod 10 on the number gives the number without the first digit and repeat that till you have all the digits

User · Answer

If its only for validating you could do  887979789  gt  99999999

User · Answer

Assuming your question was referring to an int  the following works for negative positive and zero as well   Math Floor  decimal  Math Abs n   ToString   Length

[c#] How can I get a count of the total number of digits in a number?

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