how to write toupper method in c++ code example

Example 1: string to upper c++

std::string data = "This is a sample string.";
// convert string to upper case
std::for_each(data.begin(), data.end(), [](char & c){
c = ::toupper(c);
});

Example 2: toupper c++

int result = toupper(charecterVariable);// return the int that corresponding upper case char
//if there is none then it will return the int for the original input.
//can convert int to char after
char result2 = (char)toupper(variableChar);