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C Library
cassert (assert.h)
cctype (ctype.h)
cerrno (errno.h)
cfloat (float.h)
ciso646 (iso646.h)
climits (limits.h)
clocale (locale.h)
cmath (math.h)
csetjmp (setjmp.h)
csignal (signal.h)
cstdarg (stdarg.h)
cstddef (stddef.h)
cstdio (stdio.h)
cstdlib (stdlib.h)
cstring (string.h)
ctime (time.h)
cctype (ctype.h)
isalnum
isalpha
iscntrl
isdigit
isgraph
islower
isprint
ispunct
isspace
isupper
isxdigit
tolower
toupper


isalpha

function
<cctype> 
int isalpha ( int c );

Check if character is alphabetic

Checks if parameter c is either an uppercase or a lowercase alphabetic letter.

Notice that what is considered a letter may depend on the locale being used; In the default C locale, what constitutes a letter is what returns true by either isupper or islower.

For a detailed chart on what the different ctype functions return for each character of the standard ANSII character set, see the reference for the <cctype> header.

In C++, a locale-specific template version of this function (isalpha) exists in header <locale>.

Parameters

c
Character to be checked, casted to an int, or EOF.

Return Value

A value different from zero (i.e., true) if indeed c is an alphabetic letter. Zero (i.e., false) otherwise.

Example

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/* isalpha example */
#include <stdio.h>
#include <ctype.h>
int main ()
{
  int i=0;
  char str[]="C++";
  while (str[i])
  {
    if (isalpha(str[i])) printf ("character %c is alphabetic\n",str[i]);
    else printf ("character %c is not alphabetic\n",str[i]);
    i++;
  }
  return 0;
}


Output:
character C is alphabetic
character + is not alphabetic
character + is not alphabetic

See also

isalnum Check if character is alphanumeric (function)
isdigit Check if character is decimal digit (function)