isdigit—decimal digit predicate #include <ctype.h>
int isdigit(int c);
Description
isdigit is a macro which classifies ASCII integer values by table
lookup. It is a predicate returning non-zero for decimal digits, and 0 for
other characters. It is defined only if c is representable as an
unsigned char or if c is EOF.
You can use a compiled subroutine instead of the macro definition by
undefining the macro using `#undef isdigit'.
Returns
isdigit returns non-zero if c is a decimal digit (0–9).
Portability
isdigit is ANSI C.
No supporting OS subroutines are required.