新手编程，一个关于while循环无法跳出的问题，请高手帮忙，谢谢。

#include<iostream>
#include<cctype>
using std::cin;
using std::cout;
using std::endl;
int main()
{
    int num1=0;
    int num2=0;
    double average=0;
    int yes_no=0;
    int count=0;
    while(std::tolower(yes_no)!='n')
    {
        cout<<"Enter a number please"<<endl;
             cin>>num1;
             num2+=num1;
             count++;
             cout<<"Do you want to enter anoter number"<<"("<<"y/n"<<")"<<endl;
             cin>>yes_no;
             cout<<endl;
    }
         average=num2/count;
    cout<<"The plused number is"<<num2<<endl;
    cout<<"The average number is"<<average<<endl;
    return 0;
}
        当输入了Y后进入死循环，cin语句不能正常执行非常郁闷。请帮忙解说下，我也能用其他语句解决，但是不知道为什么这样就不行。高手帮忙