C Program to Check Uppercase and Lowercase Character

A character is said to be in uppercase if it is in capital letter and it is said to be in lowercase if it is in small letter. C program to check whether an entered character is in uppercase of lowercase is shown below.

Example 1: Program to Check Uppercase / Lowercase Using ASCII value

#include<stdio.h>
int main()
{
   char c;
   
   printf ("Enter a character n");
   scanf ("%c", &c);

   if (c>64 && c<91)
   {
         printf ("It is uppercase character");   
   }     
    else
   {
         printf ("It is in lowercase character");
   }

   return 0;
}

We know that the ASCII value of lowercase alphabet ‘a’ is 97, ‘b’ is 98 … ‘z’ is 122. And the ASCII value of uppercase alphabet ‘A’ is 65, ‘B’ is 66 … ‘Z’ is 90. So the program displays whether the entered character is lowercase alphabet or uppercase alphabet by checking its ASCII value.

Another method to check in C program whether entered character is in lowercase or uppercase is by comparing the entered character with the alphabets itself. This is shown below.

Example 2: Program to Check Uppercase / Lowercase Using Character Comparison

#include<stdio.h>
int main()
{
     char c;
     printf ("Enter a character n");
     scanf ("%c", &c);

     if (c>='A' && c<='Z')
     {
         printf ("It is uppercase character");
     }
     else
     {
           printf ("It is lowercase character");
     }
     
     return 0;

}

Here, instead of remembering the ASCII value of ‘a’ or ‘A’ and ‘z’ or ‘Z’, we directly compare the entered character as c>=’A’ and c<=’Z’.

Example 3: Program to Check Uppercase / Lowercase Using Library Function isupper() and islower()

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

int main()
{
     char c;
     printf ("Enter a character n");
     scanf ("%c", &c);

     if (isupper(c))
     {
            printf ("It is UPPERCASE character");
     }
     else if (islower(c))
     {
           printf ("It is lowercase character");
     }
     else 
     {
           printf("It is not a character"); 
     }

     return 0;

}

The isupper() function returns 1 if the parameter passed is uppercase character and 0 if parameter passed is lowercase character.

The islower() function returns 1 if the parameter passed is lowercase character and 0 if parameter passed is uppercase character.

Output

Enter a character
H
It is in uppercase

Enter a character
h
It is in lowercase.