function
<cctype>

isdigit

int isdigit ( int c );
Check if character is decimal digit
Checks whether c is a decimal digit character.

Decimal digits are any of: 0 1 2 3 4 5 6 7 8 9

For a detailed chart on what the different ctype functions return for each character of the standard ASCII character set, see the reference for the <cctype> header.

In C++, a locale-specific template version of this function (isdigit) exists in header <locale>.

Parameters

c
Character to be checked, casted to an int, or EOF.

Return Value

A value different from zero (i.e., true) if indeed c is a decimal digit. Zero (i.e., false) otherwise.

Example

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/* isdigit example */
#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
int main ()
{
  char str[]="1776ad";
  int year;
  if (isdigit(str[0]))
  {
    year = atoi (str);
    printf ("The year that followed %d was %d.\n",year,year+1);
  }
  return 0;
}


Output

The year that followed 1776 was 1777

isdigit is used to check if the first character in str is a digit and therefore a valid candidate to be converted by atoi into an integer value.

See also

isalnum
Check if character is alphanumeric (function )
isalpha
Check if character is alphabetic (function )