C Library - isalpha() Function

The C ctype library isalpha() function is used to check if a given character is an alphabetic letter or not. If argument c is not an alphabetic letter, the function returns 0 (false).

Syntax

Following is the C library syntax of the isalpha() function −

int isalpha(int c);

Parameters

This function accepts a single parameter −

• c − This is the character to be checked, passed as an int. The value of c must be representable as an unsigned char or must be equal to EOF.

Return Value

The function returns a non-zero value (true) if the character c is an alphabetic letter (either uppercase or lowercase), which means it falls within the ranges A to Z or a to z.

Example 1: Checking a Single Alphabetic Character

We will take a alphabetic letter form the Character set A-Z and then check if the letter is recognized as an alphabet or not by isalpha() function.

#include <stdio.h>
#include <ctype.h>

int main() {
   char c = 'A';

   if (isalpha(c)) {
      printf("%c is an alphabetic character.\n", c);
   } else {
      printf("%c is not an alphabetic character.\n", c);
   }
   return 0;
}

Output

The above code produces following result −

A is an alphabetic character.

Example 2: Checking a special character

In this example, we check if a special character is also recognized as a alphabetic character or not.

#include <stdio.h>
#include <ctype.h>

int main() {
   char c = '@';

   if (isalpha(c)) {
      printf("%c is an alphabetic character.\n", c);
   } else {
      printf("%c is not an alphabetic character.\n", c);
   }
   return 0;
}

Output

The above code produces following result −

@ is not an alphabetic character.