C++问题， 为什么输入0.99会进入死循环

在学习C++时调试这段代码在month 输入**小于1的小数**时，进入死循环,还请大神帮忙解释一下，感谢

int userYear, userMonth;
cout<< "Please input year:"<<endl;
cin >> userYear;

cout<<"Please input month:"<<endl;
cin >> userMonth;

while(userMonth > 12 || userMonth < 1){
    cout<<"The month is not legal, Please input again: "<<endl;
    cin >> userMonth;
}
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