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>.
- Character to be checked, casted to an int, or EOF.
A value different from zero (i.e., true) if indeed c is a decimal digit. Zero (i.e., false) otherwise.
/* isdigit example */
int main ()
year = atoi (str);
printf ("The year that followed %d was %d.\n",year,year+1);
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.
- Check if character is alphanumeric (function)
- Check if character is alphabetic (function)