输入字符时，为什么程序会有无限循环？

Question

#include<iostream>
#include<cstdlib>
#include<ctime>
#include<string>

using namespace std;

int main()
{
    char replay;
    int userInput;
    cout<< "Let's play Rock, Paper, Scissors"<<endl;
  do
 { 
    cout<<"Enter 1 for Rock, 2 for Paper, 3 for Scissors"<< endl;
    cin>> userInput;

    switch(userInput)
    {
      case 1:
      cout <<"You chose rock" << endl;
      break;

      case 2:
      cout <<"You chose paper" <<endl;
      break;

      case 3:
      cout <<"You chose scissors" << endl;
      break;

      default:
      cout << userInput << " is not a valid choice"<< endl;
      break;
   }  
    cout<<"Would you like to play again (Y for yes, N for no)?"<<endl;
    cin >> replay;
 }  while((replay=='Y') || (replay=='y')); 

    return 0; 

 }

When I enter in a character in my answer for entering a number and when I'm asked if I want to play again and I enter in a character that isn't Y, y, N, or n it goes into an infinite loop

Answer 1

userInput is defined as an int . When you attempt to read an int , and what is actually in the stream is a char , it will fail (but the char is still in the buffer). You must clear the error status and ignore the bad input:

if (!(cin >> userInput))
{
    cin.clear(); // clears the error state
    cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n'); // remove the bad input from the buffer
}
else
{
    // the code if the input was valid
}

Answer 2

Just a suggestion, but I would rearrange your code as follows:

#include<iostream>
#include<cstdlib>
#include<ctime>
#include<string>

using namespace std;

int main()
{
    char replay;
    char userInputChar;
    int userInput;
    cout<< "Let's play Rock, Paper, Scissors"<<endl;
    for(;;)
    { 
        cout << "Enter 1 for Rock, 2 for Paper, 3 for Scissors"<< endl;
        cin >> userInputChar;

        userInput = userInputChar - '0';

        switch(userInput)
        {
            case 1:
            cout <<"You chose rock" << endl;
            break;

            case 2:
            cout <<"You chose paper" <<endl;
            break;

            case 3:
            cout <<"You chose scissors" << endl;
            break;

            default:
            cout << userInput << " is not a valid choice"<< endl;
            break;
        }  
        cout<<"Would you like to play again (Y for yes, N for no)?"<<endl;
        cin >> replay;

        if((replay!='Y') || (replay!='y'))
            break;
    } 

    return 0; 

 }

Notice how I took care of converting the char input to an int .

If you want to use your current loop declare userInput as a char and then make your switch statement like this: switch(userInput - '0')