isupper() Function Example in C Programming

In this source code example, we will see how to use the isupper() function in C programming with an example.

isupper() Function Overview

The isupper() function is found in the <ctype.h> library in C. This function checks whether the provided character is an uppercase alphabetic character (A-Z). 

Key Points: 

- You need to include the <ctype.h> header to utilize the function. 

- The function accepts an int, which represents the ASCII value of the character. 

- It returns a non-zero value (true) if the character is an uppercase alphabetic letter and zero (false) otherwise.

Source Code Example

#include <stdio.h>
#include <ctype.h>  // Required for isupper()

int main() {
    char ch;

    printf("Enter a character: ");
    scanf("%c", &ch);

    if (isupper(ch)) {
        printf("The character you entered is an uppercase letter.\n");
    } else {
        printf("The character you entered is not an uppercase letter.\n");
    }

    return 0;
}

Output

Enter a character: A
The character you entered is an uppercase letter.
Or
Enter a character: a
The character you entered is not an uppercase letter.

Explanation

1. The required header files are initially included: stdio.h for standard I/O functions and ctype.h for the isupper() function.

2. The main() function starts by declaring a character variable ch.

3. A prompt asks the user to input a character, which is then stored in the ch variable.

4. The isupper() function checks if the character is an uppercase alphabetic letter.

5. A message is displayed indicating whether the character is uppercase or not.