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).

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**Authoritative source**: BUSMASTER DITA help source `isdigit.dita`, compiled into `BUSMASTER.CHM` with the application.