Dice Rolling Simulation

[Lucas Martin]

I have coded a dice rolling simulation to roll a single die 36,000 times, store the data in the array and display how many times the face value landed. My question is what do I need to do to change this to simulate rolling 2 die to display the output of 2-12 face value, so adding the face value of the 2 randomly rolled die and incrementing face value. Here is the code I have for the single die:

// Dice Rolling

import java.util.Random;

public class DiceRolling
{
	public static void main( String[] args)
	{
		Random randomNumbers = new Random(); // Generates random numbers
		int[] array = new int[ 7 ]; // Declares the array
		
		//Roll the die 36,000 times
		for ( int roll = 1; roll <=36000; roll++ )
			++array[ 1 + randomNumbers.nextInt ( 6 ) ];
		
		System.out.printf( "%s%10s\n", "Face", "Frequency" );
		
		// outputs array values
		for ( int face = 1; face < array.length; face++ )
			System.out.printf( "%4d%10d\n", face, array[ face ] );
		
	} // end main
	
} // end class DiceRolling

[Greg Brannon]

So you have an array that can hold 6 values, 1 - 6, and a random number generator that generates random values 1 - 6. With two dice, the array will have to be scaled to hold the values 2 - 12 (11 total), and your random number generator will have to be modified to generate values from 2 - 12. Modifying the code you've already written should be relatively easy.

[Lucas Martin]

Greg Brannon wrote:So you have an array that can hold 6 values, 1 - 6, and a random number generator that generates random values 1 - 6. With two dice, the array will have to be scaled to hold the values 2 - 12 (11 total), and your random number generator will have to be modified to generate values from 2 - 12. Modifying the code you've already written should be relatively easy.

I thought about that, wouldn't that throw off the results of rolling 2 die with a 1-6 outcome and adding the values? I guess I am failing at the logic here.

[Matthew Brown]

Lucas Martin wrote:I thought about that, wouldn't that throw off the results of rolling 2 die with a 1-6 outcome and adding the values?

Yes, it would. You need to extend array, but then generate the index by adding together two random numbers from 1-6.

[Lucas Martin]

That answers it for me, thanks.

[Lucas Martin]

Well I thought I knew what I was doing and have spent some timeon this but apparently not. So now I am getting dice1 has not been initialized and I do not think I am summing up the two random 1,6 numbers into the total and adding them to the array correctly, any final touch ups are appreciated, thanks.

// Dice Rolling

import java.util.Random;

public class DiceRolling
{
	public static void main( String[] args)
	{
		Random randomNumbers = new Random(); // Generates random numbers
		int[] array = new int[ 13 ]; // Declares the array
		int dice1;
		int dice2;
		int total;
		
		//Roll the die 36,000 times
		for ( int roll = 1; roll <=36000; roll++ )
			dice1 = 1 + randomNumbers.nextInt ( 6 );
			dice2 = 1 + randomNumbers.nextInt ( 6 );
			total = dice1+dice2;
			++array[total];
			
		System.out.printf( "%s%10s\n", "Face", "Frequency" );
		
		// outputs array values
		for ( int face = 1; face < array.length; face++ )
			System.out.printf( "%4d%10d\n", face, array[ face ] );
		
	} // end main
	
} // end class DiceRolling

[Greg Brannon]

Matthew Brown wrote:

Lucas Martin wrote:I thought about that, wouldn't that throw off the results of rolling 2 die with a 1-6 outcome and adding the values?

Yes, it would. You need to extend array, but then generate the index by adding together two random numbers from 1-6.

Sorry, I didn't think through the subtleties. I'd have gotten it wrong.

[Lucas Martin]

I got it: I was initializing them correctly, but to my surprise I added the braces and works like a charm *forehead denter*

//Roll the die 36,000 times
		for ( int roll = 1; roll <=36000; roll++ )
		{	
			int die1 = 1 + randomNumbers.nextInt ( 6 );
			int die2 = 1 + randomNumbers.nextInt ( 6 );
			int total = die1 + die2;
			++array[total];
			
		}

[Greg Brannon]

As penance, I modified your program to include a 2nd column that shows how messed up generating the sum from a single random number would be, about what you'd expect if the random number generator does what it's supposed to do:

// Dice Rolling

import java.util.Random;

public class DiceRolling
{
    public static void main( String[] args)
    {
        Random randomNumbers = new Random(); // Generates random numbers
        int[] array = new int[ 13 ]; // Declares the array
        int[] singleArray = new int[13];
        int dice1;
        int dice2;
        int dice3;
        int total;
        
        //Roll the die 36,000 times
        for ( int roll = 1; roll <=36000; roll++ )
        {
            dice1 = 1 + randomNumbers.nextInt ( 6 );
            dice2 = 1 + randomNumbers.nextInt ( 6 );
            dice3 = 2 + randomNumbers.nextInt ( 11 );
            total = dice1 + dice2;
            ++array[total];
            ++singleArray[dice3];
        }
            
        System.out.printf( "%s%16s%15s\n", "Face", "Frequency 1", "Frequency 2" );
        
        // outputs array values
        for ( int face = 1; face < array.length; face++ )
            System.out.printf( "%3d%13d%15d\n", face, array[ face ], singleArray[face] );
        
    } // end main
    
} // end class DiceRolling

A sample run:

Face     Frequency 1    Frequency 2
  1            0              0
  2          992           3243
  3         2054           3269
  4         2949           3250
  5         4017           3213
  6         5040           3274
  7         6033           3223
  8         4886           3282
  9         3933           3357
 10         3035           3341
 11         1997           3318
 12         1064           3230

[Lucas Martin]

Exactly, the 7's are much more likely to add up from the 2 die sums and it shows this.
Well at least now it's here for people to learn from.