#include <iostream>
#include <cstdio>

int main() {
    const char* oldName = "oldname.txt";
    const char* newName = "newname.txt";
    
    if (rename(oldName, newName) == 0) {
        std::cout << "File renamed successfully." << std::endl;
    } else {
        std::cerr << "Error renaming file." << std::endl;
    }
    
    return 0;
}