function
<cctype>
isdigit
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)