toupper

#include <iostream>

#include <string>

using namespace std;

int main() {

     string a = "Hello Bill Gates.";

     for (int i = 0; i < a.length(); i++) {

          a[i] = toupper(a[i]);

     }

     cout << a;

     system("pause");

     return 0;

}

#include <iostream>

#include <string>

#include <locale>  

using namespace std;

int main() {

     string a = "Hello Bill Gates.";

     locale loc;

     for (auto elem : a)

          cout << toupper(elem, loc);

     cout << a;

     system("pause");

     return 0;

}