Simple guessing game continuing with any other letter other than the declared variable Y/N

I am a aspiring developer and I am just learning my first language which is C++. I was creating a simple guessing game using the things I've learned off of the internet and YouTube. Pretty much the computer randomly generates a number between 0 and 5 and you'll have to enter which number you would be the correct one.

The problem would be that after the program asks for your name ( Which isn't stored) then would ask if you would like to play a game which asks for a y or a n. y continues and n closes the program.

Y is suppose to continue the game but if I would put another letter, g for example, it would continue with the game. How would I fix the code to only allow the variable "y/Y" to continue the game?

Thank you for your help!

Below is the code.

#include <iostream>
#include <Windows.h>
#include <cmath>
#include <ctime>
#include <string>

using namespace std;

int main()
{
    int num, numrand;
    char yn;
    string name;
    srand(time(NULL));
    cout << "Welcome to the program and please enter your name:";
    cin >> name;
    while (true)
    {
        cout << "Hello " << name << " do you want to play a game? (y/n): ";
        cin >> yn;
        if (yn == 'n' || yn == 'N')

            return 0;
        if (yn == 'y' || yn == 'Y');
        break;
        //If any other letter is used then it will continue. how to fix?
    }

    while (true)
    {
        cout << "computer will imagine one number from 0 to 5 and you will be given the task to guess it: ";
        cin >> num;
        numrand = rand() % 6;
        if (numrand == num)
            cout << "You Win!" << endl;
        else if (num == -1)
            break;
        else
            cout << "You Lose! The computer imagined the number: "<< numrand << endl;

    }


    system("pause");
    return 0;
}