C - how to find the length of an integer

Question

I m trying to find a way to find the length of an integer  number of digits  and then place it in an integer array  The assignment also calls for doing this without the use of classes from the STL  although the program spec does say we can use  common C libraries   gonna ask my professor if I can use cmath  because I m assuming log10 num    1 is the easiest way  but I was wondering if there was another way      Ah  and this doesn t have to handle negative numbers  Solely non-negative numbers   I m attempting to create a variant  MyInt  class that can handle a wider range of values using a dynamic array  Any tips would be appreciated  Thanks

User · Answer

Would this be an efficient approach  Converting to a string and finding the length property   int num   123   string strNum   to string num      123 becomes  123  int length   strNum length       length   3 char array 3      or whatever you want to do with the length

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Being a computer nerd and not a maths nerd I d do   char buffer 64   int len   sprintf buffer    d   theNum

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Best way is to find using log  it works always  int len   ceil log10 num   1

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Code for finding Length of int and decimal number       include lt iostream gt       include lt cmath gt      using namespace std      int main                 int len num          cin  gt  gt  num          len   log10 num    1          cout  lt  lt  len  lt  lt  endl          return 0              sample input output       45566     5      Process returned 0  0x0    execution time   3 292 s     Press any key to continue

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I mean the number of digits in an integer  i e   123  has a length of 3   int i   123      the  length  of 0 is 1  int len   1      and for numbers greater than 0  if  i  gt  0           we count how many times it can be divided by 10          how many times we can cut off the last digit until we end up with 0      for  len   0  i  gt  0  len              i   i   10              and that s our  length   std  cout  lt  lt  len    outputs 3

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Not necessarily the most efficient  but one of the shortest and most readable using C     std  to string num  length

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There is a much better way to do it        include lt cmath gt              int size   trunc log10 num     1        works for int and decimal

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How about  works also for 0 and negatives    int digits  int x          return    bool  x    int  log10  abs  x       1

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The number of digits of an integer n in any base is trivially obtained by dividing until you re done   unsigned int number of digits   0   do          number of digits        n    base    while  n

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Closed formula for the longest int  I used int here  but works for any signed integral type    1    int  ceil  8 sizeof int -1    log10 2     Explanation                     sizeof int                     number bytes in int                 8 sizeof int                     number of binary digits  bits                  8 sizeof int -1                  discount one bit for the negatives                 8 sizeof int -1    log10 2       convert to decimal  because                                                   1 bit    log10 2  decimal digits      int  ceil  8 sizeof int -1    log10 2       round up to whole digits 1    int  ceil  8 sizeof int -1    log10 2       make room for the minus sign   For an int type of 4 bytes  the result is 11  An example of 4 bytes int with 11 decimal digits is   -2147483648    If you want the number of decimal digits of some int value  you can use the following function   unsigned base10 size int value        if value    0            return 1u             unsigned ret      double dval      if value  gt  0            ret   0          dval   value        else              Make room for the minus sign  and proceed as if positive          ret   1          dval   -double value              ret    ceil log10 dval 1 0         return ret      I tested this function for the whole range of int in g   9 3 0 for x86-64

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int intLength int i        int l 0      for  i i  10  l        return l  0   1   l      Here s a tiny efficient one

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If you can use C libraries then one method would be to use sprintf  e g    include  lt cstdio gt   char s 32    int len   sprintf s    d   i

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Most efficient code to find length of a number   counts zeros as well  note  n  is the number to be given    include  lt iostream gt  using namespace std  int main         int n len  0      cin gt  gt n  while n  0               len           n n 10            cout lt  lt len lt  lt endl      return 0

[c++] C++ - how to find the length of an integer

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