Thread: Dice Rolling Probability - How Do I Start It Off?

Just a quick question on how to start off a code on this. The program is supposed to simulate tossing a pair of 2-sided dice and determining the percentage of times each possible combination of the dice is rolled. The actual assignment is using 11-sided dice but I just want a simple code to start off with. I want to make it into one loop using for, if, and nested loops. How would a code like this look?

Things I Need
Loop to increment through the possible sums of the dice

for (int sum = 2; sum <= 4; sum++)

Loop to throw dice given number of times

for (int roll = 0; roll < totalRolls; roll++)

Randomly generate values for two dice

die1 = (int)(Math.random() * 10);
die2 = (int)(Math.random() * 10);
diceSum = die1 + die2;

Check if the sum of dice is equal to the given sum

Originally Posted by Norm

Not sure what the first loop (for(sum)) is supposed to do. Can you explain why sum starts at 2 and goes to 4?


That sounds like the dice should be rolled 1000s of times, each diceSum counted and then the % computed.
Say there are 3 different sums, and the dice were rolled 1000 times then the sums could be:
250, 500, 250
and the %s would be:
25, 50, 25

It's supposed to represent all the possible sums I could get from the dice. So the lowest possible number would be 2 and the highest would be 4.

If the sum on the dice is equal to the sum, then it raises by one. If not, it just goes on to the next sum and it loops for how many times the user asks for it to be rolled.

Originally Posted by Norm

Is the problem: What % of rolls produces a value given by the user? The number of rolls to make is also given by the user.

It's similar to what you said. I need to display the probability of how many times a combination will occur depending on how many rolls the user input.

For example, since I'm doing a 2-sided dice and let's say the user enters in 1 roll:

2s: 25%
3s: 50%
4s: 25%

Originally Posted by Norm

Not sure I understand what you mean by 1 roll.
If a 2 is rolled then a 2 is rolled 1/1 = 100% of the time.

I meant the user would enter in 1 as the number of rolls they want. Basically, it's like this:
-Ask the user to input how many times the dice will be rolled.
-Calculate the probability of each combination of dice.

I'm confused as how to do that. The snippets I put above are just thoughts but I'm not sure if they will actually be used.

Originally Posted by Norm

If there is only one roll, how do you compute the %? Normally there are 1000s of rolls.

I don't think you understand the problem yet.

Yeah, that was a bad example. If it was only 1 roll, then it would be 100% for one combination. I think 100 rolls would be better. So, how would I code this problem?

Okay well here's what I have so far. I'm not sure if even this is correct. How do I display the number of times it matches for each sum?

import java.util.Random;
import java.util.Scanner;
public class DiceProbability
{
    public static void main(String[] args)
    {
        Scanner in = new Scanner(System.in);
        Random randNum = new Random();
 
        int match = 0;  //Number of times sum of dice matches the current sum
        int die1, die2;
        int totalRolls = 0;
        int diceSum = 0;
 
        System.out.print("How many times do you want to roll the dice? ");
        totalRolls = in.nextInt();        
 
        //Print heading for output table
        System.out.println("Sum of Dice      Probability");
 
        for (int sum = 2; sum <= 22; sum++)
        {
            for (int roll = 0; roll < totalRolls; roll++)
            {
                die1 = randNum.nextInt(11);
                die2 = randNum.nextInt(11);
                diceSum = die1 + die2;  
            } 
 
            if (diceSum == sum)
            {
               match++;
            }
            else
            {
            }
        }
 
        //After all throws, calculate percentage of throws that resulted 
        //in the given sum.
 
        //Print results 
        System.out.println("   2s:         " + match);
        System.out.println("   3s:         ");
        System.out.println("   4s:         ");
        System.out.println("   5s:         ");
        System.out.println("   6s:         ");
        System.out.println("   7s:         ");
        System.out.println("   8s:         ");
        System.out.println("   9s:         ");
        System.out.println("   10s:        ");
        System.out.println("   11s:        ");
        System.out.println("   12s:        ");
        System.out.println("   13s:        ");
        System.out.println("   14s:        ");
        System.out.println("   15s:        ");
        System.out.println("   16s:        ");
        System.out.println("   17s:        ");
        System.out.println("   18s:        ");
        System.out.println("   19s:        ");
        System.out.println("   20s:        ");
        System.out.println("   21s:        ");
        System.out.println("   22s:        "); 
 
    } //end main
}//end class DiceProbability