C program to check whether a character is alphabet or not

Write a C program to input a character from user and check whether the given character is alphabet or not using if else. How to check whether a character is alphabet or not in C programming. Logic to check if a character is alphabet or not in C program.

Input character: a

'a' is alphabet

Required knowledge

Basic C programming, Relational operators, Logical operators, If else

Logic to check alphabets

In C every printable and non-printable symbol is treated as a character and has an ASCII value. ASCII value is unique integer value for every character. It is used to represent a character in memory. In memory every character is stored as an integer.

One of the beginner way to tackle the problem is check input for every alphabet characters. However, I will not explain this method neither I recommend you to try.

An input character is alphabet if it is in between a-z or A-Z.
Note: a and A both are different and have different ASCII values.

Step by step descriptive logic to check alphabets.

1. Input a character from user. Store it in some variable say ch.
2. Check if((ch >= 'a') && (ch <= 'z')) or if((ch >= 'A') && (ch <= 'Z')). Then it is alphabet otherwise not.

Let us implement above logic through C program.

Program to check alphabets

/**
 * C program to check whether a character is alphabet or not
 */

#include <stdio.h>

int main()
{
    char ch;
    
    /* Input a character from user */
    printf("Enter any character: ");
    scanf("%c", &ch);
    

    if((ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <= 'Z'))
    {
        printf("Character is an ALPHABET.");
    }
    else
    {
        printf("Character is NOT ALPHABET.");
    }

    return 0;
}

Note: You can also use ASCII values to check alphabets. ASCII value of a=97, z=122, A=65 and Z=90.

Program to check alphabets using ASCII value

/**
 * C program to check whether a character is alphabet or not
 */

#include <stdio.h>

int main()
{
    char ch;

    /* Input a character from user */
    printf("Enter any character: ");
    scanf("%c", &ch);


    if((ch >= 97 && ch <= 122) || (ch >= 65 && ch <= 90))
    {
        printf("Character is an ALPHABET.");
    }
    else
    {
        printf("Character is NOT ALPHABET.");
    }

    return 0;
}

Enter any character: b
Character is an ALPHABET.