CODEWITHSUNDEEP
javarandom
Minnie21
Minnie21

Reputation: 29

printing even numbers from random generator

import java.util.*;
public class Exam2_2 {
    public static void main(String[]args) {
        Random rand = new Random();
        int roll = 0;
        int roll2 = 0;
        int tries = 0;

        while((roll % 2 == 0) && (roll2 % 2 == 0)) {
            roll = rand.nextInt(8) + 1;
            roll2 = rand.nextInt(8) + 1;
            System.out.println("(" + roll + ", " + roll2 + ")");
            tries++;
        } 
        System.out.println("you won after " + tries + " tries");
    }
}

My assignment is to simulate rolling two 8-sided dice and only stop once both numbers are even. I'm not sure what I'm doing wrong and have tried a bunch of different things to see if it would work the way I need it to work. Any advice would be much appreciated. Thanks.

Upvotes: 0

Views: 62

Answers (2)

Michael Yaworski
Michael Yaworski

Reputation: 13483

The problem is in your while condition:

while( (roll % 2 == 0) && (roll2 % 2 == 0) )

That means that while roll is even and roll2 is also even, it'll do the stuff inside that block.

But, you want it to continue looping while their NOT both even, and stop when they are.

So you should change your condition to this:

while( !( (roll % 2 == 0) && (roll2 % 2 == 0) ) ) // they're NOT both even

or you could do this for better clarity:

while( (roll % 2 != 0) || (roll2 % 2 != 0) ) // at least one of them is odd

This way, the condition will be false when they're both even, thus stopping the loop.

Upvotes: 0

Elliott Frisch
Elliott Frisch

Reputation: 201439

This seems like the perfect time to use a do {} while to me, something like

Random rand = new Random();
int tries = 0;
int roll;
int roll2;
do {
    roll = rand.nextInt(8) + 1;
    roll2 = rand.nextInt(8) + 1;
    System.out.printf("(%d, %d)%n", roll, roll2);
    tries++;
} while ((roll % 2 != 0) || (roll2 % 2 != 0)); // <-- while roll or
                                               //     roll2 is odd.
System.out.println("you won after " + tries + " tries");

Or, You can use DeMorgan's Law and replace ((roll % 2 != 0) || (roll2 % 2 != 0)) with

while (!((roll % 2 == 0) && (roll2 % 2 == 0)));

that is, while NOT (roll is even and roll2 is even).

Upvotes: 2

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