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isdigit
[decimal digit predicate]

SYNOPSIS
#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 when isascii(c) is true or 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).

COMPLIANCE
isdigit is ANSI C.

No supporting OS subroutines are required.