将“yy”输入到只应采用单个字符（例如“y”或“n”）的字符变量时创建的无限循环，“nn”不会破坏代码

Question

The code in the cont function asks the user if they want to play my game again.

The code works when receiving proper character inputs such as 'y' or 'n' as well as their respective capital letter variants, and the else block works properly to loop the function if an invalid input such as 'a' or 'c' is entered.

However during a test run, an input of 'yy' breaks the code causing the program to infinitely loop, running not only this cont function but my game function as well.

choice is stored as a char variable. I am wondering why the code even continues to run upon inputting multi-character inputs such as 'yy' or 'yes' . What's interesting is 'nn', 'ny' and other variations of multi-character inputs that begin with 'n' causes no issues and properly results in the else if block running as intended. Which prints "Thanks for playing." then ends the program.

Can variables declared as char accept inputs greater than 1 character? Does it only take the first value? And if so why does 'yy' cause a loop rather than the program running as intended by accepting a value of 'y' or 'Y' ? How can I change my program so that an input of 'yy' no longer causes issues, without specific lines targeting inputs such as 'yy' or 'yes' .

#include <iostream>
#include <string> // needed to use strings
#include <cstdlib> // needed to use random numbers
#include <ctime>

using namespace std;

// declaring functions
void cont();
void game();
void diceRoll();

// variable declaration
  string playerName;
  int balance; // stores player's balance
  int bettingAmount; // amount being bet, input by player
  int guess; // users input for guess
  int dice; // stores the random number
  char choice; 

// main functions
int main()
{
  srand(time(0)); // seeds the random number, generates random number
  cout << "\n\t\t-=-=-= Dice Roll Game =-=-=-\n";
  cout << "\n\nWhat's your name?\n";
  getline(cin, playerName);
  cout << "\nEnter your starting balance to play with : $";
  cin >> balance;

  game();
  cont();
}

// function declaration
void cont()
{
  cin >> choice;
  
  if(choice == 'Y' || choice == 'y')
  {
    cout << "\n\n";
    game();
  }
  else if (choice == 'N' || choice == 'n')
  {
    cout << "\n\nThanks for playing.";
  }
  else
  {
    cout << "\n\nInvalid input, please type 'y' or 'n'";
    cont(); // calls itself (recursive function!!!)
  }
}

void game()
{
  do
  {
    cout << "\nYour current balance is $ " << balance << "\n";
    cout << "Hey, " << playerName << ", enter amount to bet : $";
    cin >> bettingAmount;
    if(bettingAmount > balance)
      cout << "\nBetting balance can't be more than current balance!\n" << "\nRe-enter bet\n";
  } while(bettingAmount > balance);

  // Get player's numbers
  do 
  {
    cout << "\nA dice will be rolled, guess the side facing up, any number between 1 and 6 : \n";
    cin >> guess;
    if(guess <= 0 || guess > 6 )
    {
      cout << "\nYour guess should be between 1 and 6\n" << "Re-enter guess:\n";
    }
  } while(guess <= 0 || guess > 6); 

  dice = rand() % 6+1;
  diceRoll();

  if (dice == guess)
  {
    cout << "\n\nYou guessed correctly! You won $" << (bettingAmount * 6);
    balance = balance + (bettingAmount * 6);
  }
  else
  {
    cout << "\n\nYou guessed wrong. You lost $" << bettingAmount << "\n";
    balance = balance - bettingAmount;
  }
  cout << "\n" << playerName << ", you now have a balance of $" << balance << "\n";
  if (balance == 0)
  {
    cout << "You're out of money, game over";
  }
  cout << "\nDo you want to play again? type y or n : \n";
  cont();
}

void diceRoll()
{
  cout << "The winning number is " << dice << "\n";
}

Answer 1

Does it only take the first value?

Yes, the >> formatted extraction operator, when called for a single char value, will read the first non-whitespace character, and stop. Everything after it remains unread.

why does 'yy' cause a loop

Because the first "y" gets read, for the reasons explained above. The second "y" remains unread.

This is a very common mistake and a misconception about what >> does. It does not read an entire line of typed input. It only reads a single value after skipping any whitespace that precedes it.

Your program stops until an entire line of input gets typed, followed by Enter , but that's not what >> reads. It only reads what it's asked to read, and everything else that gets typed in remains unread.

So the program continues to execute, until it reaches this part:

cin >> bettingAmount;

At this point the next unread character in the input is y . The >> formatted extraction operator, for an int value like this bettingAmount , requires numerical input (following optional whitespace). But the next character is not numerical. It's the character y .

This results in the formatted >> extraction operator failing. Nothing gets read into bettingAmount . It remains completely unaltered by the >> operator. Because it is declared in global scope it was zero-initialized. So it remains 0.

In addition to the >> extraction operator failing, as part of it failing it sets the input stream to a failed state. When an input stream is in a failed state all subsequent input operation automatically fail without doing anything. And that's why your program ends up in an infinite loop.

Although there is a way to clear the input stream from its failed state this is a clumsy approach. The clean solution is to fix the code that reads input.

If your intent is to stop the program and enter something followed by Enter then that's what std::getline is for. The shown program uses it to read some of its initial input.

The path of least resistance is to simply use std::getline to read all input. Instead of using >> to read a single character use std::getline to read the next line of typed in input, into a std::string , then check the the string's first character and see what it is. Problem solved.

cin >> bettingAmount;

And you want to do the same thing here. Otherwise you'll just run into the same problem: mistyped input will result in a failed input operation, and a major headache.

Why do you need this headache? Just use std::getline to read text into a std::string , construct a std::istringstream from it, then use >> on the std::istringstream , and check its return value to determine whether it failed, or not. That's a simple way to check for invalid input, and if something other than numeric input was typed in here, you have complete freedom on how to handle bad typed in input.