isalpha

In C programming, isalpha( ) function checks whether a character is an alphabet(a to z and A-Z) or not. If a character passed to isalpha( ) is an alphabet, it returns non-zero integer if not it returns 0.

Defined in Header file: <ctype.h>

Function Prototype of isalpha( )

int isalpha(int argument);

Function isalpha() takes single argument in form of an integer and returns integer value. Even though, isalpha( ) takes integer as an argument, character is passed to isalpha( ) function. When character is passed as an argument, corresponding ASCII value of that character is passed instead of that character itself.

Example to Demonstrate the Working of isalpha( )

#include <stdio.h>
#include <ctype.h>
int main()
{
    char c;
    c='Q';
    printf("\nResult when uppercase alphabet is passed: %d",isalpha(c));
    c='q';
    printf("\nResult when lowercase alphabet is passed: %d",isalpha(c));
    c='+';
    printf("\nResult when non-alphabetic character is passed: %d",isalpha(c));
    return 0;
}

Output

Result when uppercase alphabet is passed: 1
Result when lowercase alphabet is passed: 2
Result when non-alphabetic character is passed: 0

Note: You can get different non-zero integer when alphabetic character is passed to isalpha( ) on you system. But, when you pass non-alphabetic character to isalpha( ), it always returns 0.

C Program to Check whether a Character Entered by User is Alphabet or not

#include <stdio.h>
#include <ctype.h>
int main()
{
    char c;
    printf("Enter a character: ");
    scanf("%c",&c);
    if (isalpha(c)==0)
    {
         printf("%c is an alphabet.",c);
    }
    else
         printf("%c is not an alphabet.",c);
    return 0;
}

Output

Enter a character: 5
5 is not an alphabet.