C program to check whether a character is Uppercase or Lowercase

Write a C program to input character from user and check whether character is uppercase or lowercase alphabet using if else. How to check uppercase and lowercase using if else in C programming. Logic to check uppercase and lowercase alphabets in C program.

Input character: C

'C' is uppercase alphabet

Required knowledge

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

Logic to check uppercase and lowercase alphabets

Step by step descriptive logic to check uppercase and lowercase alphabets.

1. Input a character from user. Store it in some variable say ch.
2. Character is uppercase alphabet if(ch >= 'A' and ch <= 'Z').
3. Character is lowercase alphabet if(ch >= 'a' and ch <= 'z').
4. If none of the above conditions met, then character is not alphabet.

Program to check uppercase or lowercase alphabets

/**
 * C program to check whether a character is uppercase or lowercase 
 */

#include <stdio.h>

int main()
{
    char ch;

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


    if(ch >= 'A' && ch <= 'Z')
    {
        printf("'%c' is uppercase alphabet.", ch);
    }
    else if(ch >= 'a' && ch <= 'z')
    {
        printf("'%c' is lowercase alphabet.", ch);
    }
    else
    {
        printf("'%c' is not an alphabet.", ch);
    }

    return 0;
}

You can also use inbuilt library function isupper() and islower() to check uppercase and lowercase alphabets respectively. These functions are present in ctype.h header file. Both function returns 1 if given character is uppercase or lowercase respectively otherwise returns 0.

Program to check uppercase or lowercase characters using library functions

/**
 * C program to check whether a character is uppercase 
 * or lowercase using inbuilt library functions
 */

#include <stdio.h>
#include <ctype.h> /* Used for isupper() and islower() */

int main()
{
    char ch;

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

    if(isupper(ch))
    {
        printf("'%c' is uppercase alphabet.", ch);
    }
    else if(islower(ch))
    {
        printf("'%c' is lowercase alphabet.", ch);
    }
    else
    {
        printf("'%c' is not an alphabet.", ch);
    }

    return 0;
}

The statement if(isupper(ch)) is equivalent to if(isupper(ch) == 1).

Enter any character: C
'C' is uppercase alphabet.

Happy coding 😉