**`isalpha()`** is a function in C that is used to check if the argument passed to it is in the alphabet. If the argument is not in the alphabet, then the function will return a zero, ​else it returns a non-zero value.

# How `isalpha()` works


`isalpha()` takes in an argument and converts it to ASCII. If the ASCII value is between 65 and 90 *or* between 97 and 122, it returns a non-zero value. If the ASCII​ value is out of these two ranges, zero is ​returned. 

# Code
The following code takes an array of characters and checks to see if the characters are in the alphabet​ or not:

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

int main() 
{ 
    char str[5] = {'%','&','7','A','t'}; 
    int arr[5]={0,0,0,0,0}; //to place the return values of all 
                            //characters stored in str array.

    for (int i=0;i<5;i++)
    {
      arr[i]= isalpha(str[i]);
    }
    for (int i=0;i<5;i++)
    {
      printf( "\nCharacter ");
      printf("%c", str[i]);
      if (arr[i]!=0)
      printf( " is an Alphabetic");
      else  printf( " is NOT an Alphabetic");
    }
    return 0; 
} 

What is the isalpha function in C?

isalpha() is a function in C that is used to check if the argument passed to it is in the alphabet. If the argument is not in the alphabet, then the function will return a zero, ​else it returns a non-zero value. 

What is the isalpha function in C?

How isalpha() works

Code

How `isalpha()` works