isdigit - test for a decimal digit
int isdigit(int c);
The isdigit() function tests whether c is a character of class digit in the program's current locale, see the Locale specification.
In all cases c is an int, the value of which must be a character representable as an unsigned char or must equal the value of the macro EOF. If the argument has any other value, the behaviour is undefined.
The isdigit() function returns non-zero if c is a decimal digit; otherwise it returns 0.
No errors are defined.
To ensure applications portability, especially across natural languages, only this function and those listed in the SEE ALSO section should be used for character classification.
isalnum(), isalpha(), iscntrl(), isgraph(), islower(), isprint(), ispunct(), isspace(), isupper(), isxdigit(), <ctype.h>.
Derived from Issue 1 of the SVID.