C Sharp —

Breaking Out of Infinite Loops

Another use for the break statement is to create an infinite loop in which control is transferred out of the loop only by a break statement being reached. The following example illustrates a method of writing the number-guessing game presented earlier in the chapter with a break statement used to quit the loop once the user enters the letter Q. Notice that I changed the while statement to while(true) such that it will not end until a break statement is encountered.

using System;
class InfiniteLoopApp
{
    const int MIN = 1;
    const int MAX = 10;
    const string QUIT_CHAR = "Q";
    public static void Main()
    {
        Random rnd = new Random();
        double correctNumber;
        string inputString;
        int userGuess;
        bool correctGuess = false;
        bool userQuit = false;
        while(true)
        {
            correctNumber = rnd.NextDouble() * MAX;
            correctNumber = Math.Round(correctNumber);
            Console.Write
                ("Guess a number between {0} and {1}...({2} to quit)",
                MIN, MAX, QUIT_CHAR);
            inputString = Console.ReadLine();
            if (0 == string.Compare(inputString, QUIT_CHAR, true))
            {
                userQuit = true;
                break;
            }
            else
            {
                userGuess = inputString.ToInt32();
                correctGuess = (userGuess == correctNumber);
                if ((correctGuess = (userGuess == correctNumber)))
                {
                    break;
                }
                else
                {
                    Console.WriteLine
                        ("The correct number was {0}\n", correctNumber);
                }
            }
        }
        if (correctGuess && !userQuit)
        {
            Console.WriteLine("Congratulations!");
        }
        else
        {
            Console.WriteLine("Maybe next time!");
        }
    }
}

One last point: I could have used an empty for statement here with the form for (;;) instead of while(true). They work the same, so it comes down to a matter of taste.