Dice program giving wrong numbers

Question

In class we studied some source code that used random number generation to help play the dice game known as craps. The rules of the basic game we covered in class and may be summarized as follows. The first roll of the dice ends in a win or a loss or a requirement to continue to throw the dice. If the first roll is a 7 or 11 it is a win. If the first roll is a 2, 3, or 12 it is a loss. For any other total (the point as it is called) you must rethrow the dice until you either repeat the point or throw a 7. If a rethrow generates a 7 it is a loss. If a rethrow produces the point it is a win. If neither occurs you must continue to rethrow. The source code is visible on the course web site in the Examples section. The program is titled CrapsGame.java. For this question you are to use the basic game playing code to run a simulation of 10 million games and gather some statistics from the simulation and then display the results.

The statistical information to determine and then to print out is:

• Average # of rolls per game
• The maximum number of rolls used in a single game
• The number of games that needed more than 30 rolls
• The number of wins
• The number of losses
• The probability of a win (displayed to 4 decimal places)

(THIS IS THE QUESTION)

public class CrapsGame{


public static void main(String[] args) {

int time; //number of times the game user want to play
int rolls=0; //number of rolls
int mypoint=0; 
int d1; //number user rolled for first dice
int d2; //number user rolled for second dice
int total=0; //total number of rolls 
int Numwins=0; //number of wins
int Numlosses = 0; //number of losses
double averolls=0;  //average number of rolls per game
double probwin=0; //probability of win
boolean win, rollagain=false;                  

win = false;
System.out.println("Enter the number of times the game you want to play: ");
time=TextIO.getlnInt();   

rolls=0;


for (int i=0; i<time; i++){
      d1=(int)(6*Math.random())+1; //user roll dice(generate a random number)
      d2=(int)(6*Math.random())+1;  
      System.out.printf("%d and %d\n",d1,d2);
      rolls++;
      total = total + rolls;
   switch (d1+d2) {
      case 7: 
      case 11:
        win=true; //when first roll is 7 or 11, player win
         Numwins++;
        break;
      case 2: 
      case 3: 
      case 12:
        win=false; //when first roll is 2,3 or 12, player lose
         Numlosses++;
        break;
      default:   
        mypoint = d1 + d2;
        rollagain=true; //when first roll is 1,4,5,6,8,9,10 or 11, player rethrow dice      
   }
        while(rollagain==true){
          d1=(int)(6*Math.random())+1;
          d2=(int)(6*Math.random())+1;
           System.out.printf("%d and %d\n",d1,d2);

      if (d1+d2 == mypoint ){
        win=true;
        rollagain=false;           
      }
      else if ( d1+d2 == 7){
        win=false;
        rollagain=false;  
      }
    }


 if (win){
  System.out.printf("***WINNER***\n");
 }
  else{
  System.out.printf("YOU LOSE\n");


  }



  }


probwin = Numwins / time;
averolls = total / time ;

System.out.printf("Avg # rolls: %.2f\n",averolls);
System.out.printf("Max # rolls: %d\n",rolls);
System.out.printf("# of wins: %d\n",Numwins);
System.out.printf("# of losses: %d\n",Numlosses);
System.out.printf("The probability of a win: %.2f.\n",probwin);



}
}

Here are the questions sirs! my program can run but the calculation part, every single calculation part ex. average rolls per game, number of wins and losses , etc. , doesnt work well. it always gives me wrong numbers. please help me.

Answer 1

• Instead of rolls = 0; you should do rolls = 1; since you have just made your first roll at this point.
• Your do loop is always executed at least once, that is, even when a win or loss has been determined in the first roll before the loop. Use a while loop instead.
• You are doing total = total + rolls; inside your inner loop, that is, way too often, so you end up with a too high total. Instead do it after the while loop (the do loop in your code).
• I mean what I said in the comments: mypoint holds the points from your first roll. You want the points from the roll just before this one. As the last statement inside the while loop insert mypoint = d1 + d2; to pick up the points from the roll you just made.
• You are incrementing Numwins or Numlosses only after your for loop so only the last game is counted. Move this inside your for loop instead.
• Finally, as I said in the other comment, convert your numbers to double before dividing to obtain floating-point division, for example probwin = (double) Numwins / (double) time; (technically it suffices to put (double) before one of the numbers, but I think it’s clearer what is going on if you put it in both places).

General tips:

• Don’t declare a variable until the point where you need it. It makes for more readable code and fewer errors. For example, if you had declared win inside the for loop, where you need it, you could not have made the bug of only testing it outside the for loop.
• Keep your indentation correct. Then it’s much easier to make sure whether a certain statement is inside or outside a certain loop and spot errors where a statement is in the wrong place. Your IDE can do your indentation for you at a keypress.

And finally, you didn’t ask about this, but allow me to mention anyway: Your program contains many correct things, the bugs are really details. It was easy to follow your intention, this is important in programming and certainly not always the case. Keep it that way and you will be doing fine.