How do I change the case of a string in C++?

Question

I have a string that may contain numbers as well as upper and lower case letters. I need to convert all the uppercase letters to lowercase and vice versa. How would one go about this?

Answer 1

Here's a way to do it without boost:

#include <string>
#include <algorithm>
#include <cctype>
#include <iostream>

char change_case (char c) {
    if (std::isupper(c)) 
        return std::tolower(c); 
    else
        return std::toupper(c); 
}

int main() {
    std::string str;
    str = "hEllo world";
    std::transform(str.begin(), str.end(), str.begin(), change_case);
    std::cout << str;
    return 0;
}

Answer 2

Iterate the string and use isupper() to determine if each character is uppercase or not. If it's uppercase, convert it to lowercase using tolower(). If it's not uppercase, convert it to uppercase using toupper().