Computer Science 101 Lab 4: Loops, Craps, and the Game of Nim
Due: February 18, 2002

Part 1. Exercising the Craps Program

import cs1.Keyboard;
public class craps {
// Program to simulate playing several games of craps with the user
// Authors: CS105 class              Date: February 12, 2002

  public static void main(String[] args) {
  // variable declarations
     int die1, die2, roll, firstroll;
                     // Each die is a random integer from 1-6; each of
                     // 'roll' and 'firstroll' is the sum of two dice.
     char game = 'y';             // User decides when to quit playing
     System.out.println("Welcome to craps!");
     // Each time through the loop, play one game and display the result
     while (game == 'y') {
        // compute first roll
        die1 = (int)(Math.random()*6 + 1);
        die2 = (int)(Math.random()*6 + 1);
        firstroll = die1 + die2;

        // check for immediate win or loss (and display result)
        if (firstroll == 7 || firstroll == 11)
           System.out.println("You rolled " + firstroll + " and won!");
        else if (firstroll == 2 || firstroll == 3 || firstroll == 12)
           System.out.println("You rolled " + firstroll + " and lost!");
        else {
        // if not, continue rolling (and display intermediate rolls)
           System.out.print("You rolled " + firstroll);
           die1 = (int)(Math.random()*6 + 1);
           die2 = (int)(Math.random()*6 + 1);
           roll = die1 + die2;        
           while (roll != firstroll && roll != 7) {
              System.out.print(", " + roll);
              die1 = (int)(Math.random()*6 + 1);
              die2 = (int)(Math.random()*6 + 1);
              roll = die1 + die2;          
           } // end of while loop
           System.out.print(", " + roll);
           if (roll == firstroll)
              System.out.println(" and made your point!");
           else
              System.out.println(" and crapped out!");
        }
        System.out.println("Want to play again? (y/n)");
        game = Keyboard.readChar();
     } // end of while loop
  }
}

Below is the result of a sample run of this program in which the user wants to play exactly 10 games.  Hmmm... two wins and 8 losses... looks like a very bad day at the tables!

Part 1 Questions

1. Run the program once yourself, playing 5 games.  Do you get the same results as above?  Explain.
2. How would you change the program so that it keeps track of the user's total number of wins and losses, and then reports that number at the end of the run?  For the above example, the program should display the message at the end:

You won 3 games and lost 2.


3. How would you alter the program so that it learns the user's name at the outset, and then addresses the user by name at the end of each game?  For example, the following message and response would precede the first line above:

Welcome to craps! Please enter your name:
Allen

And at the beginning of each new game, the user would be addressed by name, as in:

Want to play again, Allen?

Part 2. Game of Nim

Step 1 - Design a Program to Monitor the Game

Before writing this program, it is useful to sit down and determine its overall design by answering for yourself the following questions:

1. What are the key variables in your program, and what are their uses?
2. What kind of loop is required to control the playing of a series of games, and how will it terminate?
3. For a single game of Nim, two moves are needed - one for the user and one for the computer.  The computer's move is dictated by a random number generated in the range 1 - 3.  Both moves must be subtracted from the total number of coins that remain before the game continues.
4. What kind of loop is required to control the playing of a series of moves within a single game?  When will it terminate?  How will the program determine who wins when this loop terminates?

A typical dialog between the program and the user should look like this:  

Step 2 - Type and Run the Program

When you type your program, it should be saved with a file name that identifies you uniquely, such as lab4atucker.java . Be sure to add this program to your project (in place of the craps.java program) before you run it.

Step 3 - Debugging

As you test the program, try using the Debug option to single-step through it and observe the values of the variables as they change.  Also, observe how control changes from one method to another as you enter and return from each call.

Step 4 (Optional) - A Perfect Strategy?

Rather than use a random number to govern the computer's next move, is there a better strategy that can be used to guarantee that the computer never loses?  If so, how would you alter the program so the computer never loses?

Lab 4 Deliverables