The following code example is taken from the book
The C++ Standard Library - A Tutorial and Reference
by Nicolai M. Josuttis, Addison-Wesley, 1999
© Copyright Nicolai M. Josuttis 1999
#include <string>
#include <iostream>
#include <algorithm>
#include <cctype>
using namespace std;
int main()
{
// create a string
string s("The zip code of Hondelage in Germany is 38108");
cout << "original: " << s << endl;
// lowercase all characters
transform (s.begin(), s.end(), // source
s.begin(), // destination
tolower); // operation
cout << "lowered: " << s << endl;
// uppercase all characters
transform (s.begin(), s.end(), // source
s.begin(), // destination
toupper); // operation
cout << "uppered: " << s << endl;
}