string first_name { "Time" };
    string second_name { "Machine" };
    char first_n[100] = { "Hello" };
    char second_n[100] = { "World" };

    // METHOD 1: uses  header
    cout << first_name + second_name << endl;
    // METHOD 2: uses  header
    cout << strcat(first_n, second_n) << endl;
    // METHOD 3: uses  header
    cout << first_name.append(second_name) << endl;