función isupper() en lenguaje C

La función isupper() en la programación C verifica si el carácter dado está en mayúsculas o no. La función isupper() se define en el archivo de encabezado ctype.h. 
 

Sintaxis:  

int isupper ( int x );

Ejemplos:  

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 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");
}

Producción: 

Entered character is uppercase character

Aplicación: la función isupper() en el lenguaje de programación C se usa para averiguar el número total de mayúsculas presentes en una oración dada. 
Ejemplo: 

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 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;
}

Producción:  

Number of upper case present in the sentence is : 3