Char变量作为Y / N问题的输入

Good day! I'm a beginner in programming C++ language so pardon me for my question. The scenario: I'm asking the user if he/she wants a drink. The only answer the user can type is 'Y' for yes and 'N' for no then there comes the final dialogue. I made the answer a char: char answer; then added an if statement. If the user types Y or N, everything's fine. However, whenever the user types Y(+ any letter) such as (YHTY), the program still accepts it (same goes for N). I just need a single letter answer Y or N and other answer beyond that would lead to the else dialogue.


    #include <iostream>

    using namespace std;

    int main()
        char answer;

        cout << "Do you want a drink? " << endl;
        cout << "Y/N: ";
        cin >> answer;

        if(answer == 'Y' || answer == 'y'){
            cout << "Okay. I'll bring you some." << endl;
        }   else if(answer == 'N' || answer == 'n'){
            cout << "Okay suit yourself." << endl;
        }   else{
            cout << "Please type just Y/N." << endl;
        return 0;