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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).

COMPLIANCE
isalpha is ANSI C.

No supporting OS subroutines are required.