isupper() function in C Language

isupper() function in C programming checks whether the given character is upper case or not. isupper() function is defined in ctype.h header file. 

Syntax :

int isupper ( int x );

Examples:

Input: A
Output: Entered character is uppercase character
Input: a
Output: Entered character is not uppercase character
Input: 1
Output: Entered character is not uppercase character

C

// C program to demonstrate
// isupper() function
#include <ctype.h>
#include <stdio.h>
int main()
{
    char ch = 'A';

    // checking uppercase
    if (isupper(ch))
        printf("\nEntered character is uppercase character");
    else
        printf("\nEntered character is not uppercase character");
}

Output: 

Entered character is uppercase character

Application : isupper() function in C programming language is used to find out total number of uppercase present in a given sentence. 
Example:

Input: GEEKSFORGEEKS
Output: Number of upper case present in the sentence is : 13
Input: GeeksFORGeeks
Output: Number of upper case present in the sentence is : 5
Input: geeksforgeeks
Output: Number of upper case present in the sentence is : 0 

C

// C program to demonstrate
// isupper() function

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

// called function
int ttl_upper(int i, int counter)
{
    char ch;
    char a[50] = "GeeksForGeeks";
    ch = a[0];

    // counting of upper case
    while (ch != '\0') {
        ch = a[i];
        if (isupper(ch))
            counter++;

        i++;
    }

    // returning total number of upper case present in sentence
    return (counter);
}
int main()
{
    int i = 0;
    int counter = 0;

    // calling function
    counter = ttl_upper(i, counter);
    printf("\nNumber of upper case present in the sentence is : %d", counter);
    return 0;
}

Output: 

Number of upper case present in the sentence is : 3