（Java）使用嵌套循环

Question

My assignment instructions are "rolling" 2 dice and getting the sum and then finding the probability that that sum came up based on how many times the user wants to roll the die. I must use a nested loop and I can't use separate loops for each dice combination (which I haven't done). I am not allowed to use arrays in this assignment.

Write a program to simulate tossing a pair of 11-sided dice and determine the percentage of times each possible combination of the dice is rolled.

1. Create a new project called 5.05 Random Dice in the Mod05 Assignments folder.
2. Create a class called DiceProbability in the newly created project folder.
3. Ask the user to input how many times the dice will be rolled.
4. Calculate the probability of each combination of dice. (You may want to start with more familiar six-sided dice.)
5. Print the results neatly in two columns

I need help in finding out what I put into the second "for" loop. Sorry for the messy list of integers and if statements. The code is unfinished.

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 count2 = 0;
    int count3 = 0;
    int count4 = 0;
    int count5 = 0;
    int count6 = 0;
    int count7 = 0;
    int count8 = 0;
    int count9 = 0;
    int count10 = 0;
    int count11= 0;
    int count12= 0;
    int count13 = 0;
    int count14 = 0;
    int count15 = 0;
    int count16 = 0;
    int count17 = 0;
    int count18 = 0;
    int count19 = 0;
    int count20 = 0;
    int count21 = 0;
    int count22 = 0;
    int die1 = 0, die2 = 0;
    int rolls = 0;
    int actualDiceSum;
    double probabilityOfDice = 0.0;

    System.out.print("Number of Rolls: ");
    rolls = in.nextInt();

    for(int timesRolled = 0; timesRolled < rolls; timesRolled++)
        {
        die1 = randNum.nextInt(12);
        die2 = randNum.nextInt(12);
        actualDiceSum = die1 + die2;
        for()
        {
            if(actualDiceSum == 2){
            count2++;
            probabilityOfDice = count2 / rolls;
            }
            else if(actualDiceSum == 3){
            count3++;
            probabilityOfDice = count3 / rolls;
            }
            else if(actualDiceSum == 4){
            count4++;
            probabilityOfDice = count4 / rolls;
            }
            else if(actualDiceSum == 5){
            count5++;
            probabilityOfDice = count5 / rolls;
            }
            else if(actualDiceSum == 6){
            count6++;
            probabilityOfDice = count6 / rolls;
            }
            else if(actualDiceSum == 7){
            count7++;
            probabilityOfDice = count7 / rolls;
            }
            else if(actualDiceSum == 8){
            count8++;
            probabilityOfDice = count8 / rolls;
            }
            else if(actualDiceSum == 9){
            count9++;
            probabilityOfDice = count9 / rolls;
            }
            else if(actualDiceSum == 10){
            count10++;
            probabilityOfDice = count10 / rolls;
            }
            else if(actualDiceSum == 11){
            count11++;
            probabilityOfDice = count11 / rolls;
            }
            else if(actualDiceSum == 12){
            count12++;
            probabilityOfDice = count12 / rolls;
            }
            else if(actualDiceSum == 13){
            count13++;
            probabilityOfDice = count13 / rolls;
            }
            else if(actualDiceSum == 14){
            count14++;
            probabilityOfDice = count14 / rolls;
            }
            else if(actualDiceSum == 15){
            count15++;
            probabilityOfDice = count15 / rolls;
            }
            else if(actualDiceSum == 16){
            count16++;
            probabilityOfDice = count16 / rolls;
            }
            else if(actualDiceSum == 17){
            count17++;
            probabilityOfDice = count17 / rolls;
            }
            else if(actualDiceSum == 18){
            count18++;
            probabilityOfDice = count18 / rolls;
            }
            else if(actualDiceSum == 19){
            count19++;
            probabilityOfDice = count19 / rolls;
            }
            else if(actualDiceSum == 20){
            count20++;
            probabilityOfDice = count20 / rolls;
            }
            else if(actualDiceSum == 21){
            count21++;
            probabilityOfDice = count21 / rolls;
            }
            else if(actualDiceSum == 22){
            count22++;
            probabilityOfDice = count22 / rolls;
           }
        }
    }


    System.out.println("Sum of Dice \t\t Probability");
    System.out.println("2's\t\t" + probabilityOfDice + "%");
    System.out.println("3's\t\t" + probabilityOfDice + "%");
    System.out.println("4's\t\t" + probabilityOfDice + "%");
    System.out.println("5's\t\t" + probabilityOfDice + "%");
    System.out.println("6's\t\t" + probabilityOfDice + "%");
    System.out.println("7's\t\t" + probabilityOfDice + "%");
    System.out.println("8's\t\t" + probabilityOfDice + "%");
    System.out.println("9's\t\t" + probabilityOfDice + "%");
    System.out.println("10's\t\t" + probabilityOfDice + "%");
    System.out.println("11's\t\t" + probabilityOfDice + "%");
    System.out.println("12's\t\t" + probabilityOfDice + "%");
    System.out.println("13's\t\t" + probabilityOfDice + "%");
    System.out.println("14's\t\t" + probabilityOfDice + "%");
    System.out.println("15's\t\t" + probabilityOfDice + "%");
    System.out.println("16's\t\t" + probabilityOfDice + "%");
    System.out.println("17's\t\t" + probabilityOfDice + "%");
    System.out.println("18's\t\t" + probabilityOfDice + "%");
    System.out.println("19's\t\t" + probabilityOfDice + "%");
    System.out.println("20's\t\t" + probabilityOfDice + "%");
    System.out.println("21's\t\t" + probabilityOfDice + "%");
    System.out.println("22's\t\t" + probabilityOfDice + "%");
}
}

Answer 1

I think you need to use two dimensional array as below:

int rolls = 0;
System.out.print("Number of Rolls: ");
rolls = in.nextInt();

int[][] numAndOccuranceCount= new int[11][2]; //sum will be between 2 -12

//initialize your array
for(int indx=0; indx<11;indx++){
   numAndOccuranceCount[indx] = new int[]{indx+2,0);
} 

for(int timesRolled = 0; timesRolled < rolls; timesRolled++){
    die1 = randNum.nextInt(12);
    die2 = randNum.nextInt(12);
    actualDiceSum = die1 + die2;

    for(int indx=0; indx<11;indx++){
       if(actualDiceSum == numAndOccuranceCount[i][0]){
          numAndOccuranceCount[indx][1] = numAndOccuranceCount[indx][1]+1;
          break;
       }
    }
 }

 double proabability = 0.0;
 //compute and print the probablity as below:
  for(int indx=0; indx<11;indx++){
     proabability = numAndOccuranceCount[indx][1]/rolls;
     System.out.println("Probability of "+ numAndOccuranceCount[indx][0] +" = "+proabability);
  }

Answer 2

I have some comment on your code.

Based on the instruction, you sum up the dice1 and dice2 is not a correct approach 'cause 1 + 5 = 2 + 4 = 3 + 3 but they are different. So we have to calculate the possibility based on the combination, not the sum.

Here's my code:

DTO class:

public class DiceCombination {
    private int dice1;
    private int dice2;

    public DiceCombination(int dice1, int dice2) {
        this.dice1 = dice1;
        this.dice2 = dice2;
    }
    /* (non-Javadoc)
     * @see java.lang.Object#toString()
     */
    @Override
    public String toString() {
        return "Combination of [dice " + dice1 + " and dice " + dice2 + "]";
    }
    /* (non-Javadoc)
     * @see java.lang.Object#hashCode()
     */
    @Override
    public int hashCode() {
    final int prime = 31;
    if(dice1 < dice2) {
        return prime*dice1 + dice2;
    }
    else {
        return prime*dice2 + dice1;
    }
}
    /* (non-Javadoc)
     * @see java.lang.Object#equals(java.lang.Object)
     */
    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        DiceCombination other = (DiceCombination) obj;
        if ((dice1 == other.dice1 && dice2 == other.dice2) || (dice1 == other.dice2 && dice2 == other.dice1))
            return true;
        return false;
    }

}

Main class:

public class Posibility {

 public static void main(String[] args) {
    Map<DiceCombination,Integer> possibility = new HashMap<DiceCombination,Integer>();
    int dice1;
    int dice2;
    int roll = 400; // value here should be inputted from user, you may change any value you want
    Random randNum = new Random();

    for(int i = 0; i < roll; i ++) {
        dice1 = randNum.nextInt(12);
        dice2 = randNum.nextInt(12);
        DiceCombination dc = new DiceCombination(dice1, dice2);
        if(possibility.containsKey(dc)) {
            possibility.put(dc , possibility.get(dc) + 1); 
        }
        else {
            possibility.put(dc, 1);
        }
    }
    for(DiceCombination key : possibility.keySet()) {
        System.out.println("Result: " + key.toString() + " is " + ((double)possibility.get(key)/roll));
    }
 }
}

Answer 3

I agree with @Thinhbk that the question is technically worded in terms of combinations not sums but the picture in the link shows sums so I believe sums is the intention. The combinations approach as you have coded is impressive but too advanced for what appears to be an intro course to Java. I like how the picture shows that the IDE is BlueJ. Takes me back. Anyway, the assignment description doesn't specify the need for an inner for loop. I see @user1713336's edit that arrays are not allowed else before your (user1713336's) first loop you could add:

int[] count = new int[23];
//0 is the default value for each
//int[22] is the 23rd value in the array

What is your entire inner for loop could be replaced with:

count[actualDiceSum]++;

Then while printing in a for loop, print count[i]/rolls*100 and start int i at 2, the lowest possible value. I suspect you'll learn arrays next so I wanted to show how it'd be done.

Since you can't use arrays, your countx = 0; lines are fine as is. Don't calculate the probability in real time. It's unnecessarily and and adds many lines of code, just keep track of the number of times each value is rolled so:

if(actualDiceSum == 2)
    count2++;
else if(actualDiceSum == 3)
    count3++;
//etc 

Note that you don't need to use {} if only one line of code is tied to the if or while statement as shown. Then print the same way as before, count2/rolls*100 (Multiply by 100 since the picture showed percentages, not ratios).

Answer 4

Well according to me you don't require 2nd for loop. Every time a dice is rolled you calculate the the sum and increase the count according to the sum.

you would require to use separate variables for calculating the probability of each sum.

For example

Probability of count2 = (count2/number of rolls);
Probability of count3 = (count2/number of rolls);

Use separate variables for probability of counts

try this code

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 count2 = 0;
int count3 = 0;
int count4 = 0;
int count5 = 0;
int count6 = 0;
int count7 = 0;
int count8 = 0;
int count9 = 0;
int count10 = 0;
int count11= 0;
int count12= 0;
int count13 = 0;
int count14 = 0;
int count15 = 0;
int count16 = 0;
int count17 = 0;
int count18 = 0;
int count19 = 0;
int count20 = 0;
int count21 = 0;
int count22 = 0;
int die1 = 0, die2 = 0;
int rolls = 0;
int actualDiceSum;
double probabilityOfDice = 0.0;

System.out.print("Number of Rolls: ");
rolls = in.nextInt();

for(int timesRolled = 0; timesRolled < rolls; timesRolled++)
    {
    die1 = randNum.nextInt(12);
    die2 = randNum.nextInt(12);
    actualDiceSum = die1 + die2;

        if(actualDiceSum == 2){
        count2++;

        }
        else if(actualDiceSum == 3){
        count3++;

        }
        else if(actualDiceSum == 4){
        count4++;

        }
        else if(actualDiceSum == 5){
        count5++;

        }
        else if(actualDiceSum == 6){
        count6++;

        }
        else if(actualDiceSum == 7){
        count7++;

        }
        else if(actualDiceSum == 8){
        count8++;

        }
        else if(actualDiceSum == 9){
        count9++;

        }
        else if(actualDiceSum == 10){
        count10++;

        }
        else if(actualDiceSum == 11){
        count11++;

        }
        else if(actualDiceSum == 12){
        count12++;

        }
        else if(actualDiceSum == 13){
        count13++;

        }
        else if(actualDiceSum == 14){
        count14++;

        }
        else if(actualDiceSum == 15){
        count15++;

        }
        else if(actualDiceSum == 16){
        count16++;

        }
        else if(actualDiceSum == 17){
        count17++;

        }
        else if(actualDiceSum == 18){
        count18++;

        }
        else if(actualDiceSum == 19){
        count19++;

        }
        else if(actualDiceSum == 20){
        count20++;

        }
        else if(actualDiceSum == 21){
        count21++;

        }
        else if(actualDiceSum == 22){
        count22++;

       }
    }
}


System.out.println("Sum of Dice \t\t Probability");
System.out.println("2's\t\t" + count2/rolls + "%");
System.out.println("3's\t\t" + count3/rolls + "%");
System.out.println("4's\t\t" + count4/rolls + "%");
System.out.println("5's\t\t" + count5/rolls + "%");
//and so on...
}
}