Solution: Erase the Capital Letters

#include <iostream>
#include <string>
int main() {
    std::string str{"Only For TesTing PurPose."};
    std::cout << "str: " << str << std::endl;
    
    std::erase_if( str, [](char c){ return std::isupper(c); });
    std::cout << "str: " << str << std::endl;
}