isalpha : alphabetic character predicate

Synopsis

#include <ctype.h>
int isalpha(int c);
```### Description

isalpha is a macro which classifies ASCII integer values by table lookup. It is a predicate returning non-zero when c represents an alphabetic ASCII character, and 0 otherwise. 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 isalpha'.### Returns

isalpha returns non-zero if c is a letter (A--Z or a--z).

---

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