Question

I have a program meant to simulate some probability problem (A variation of the monty hall problem if your interested).

The code is expected to produce 50% after enough iterations but in java it always comes to 60% (even after 1000000 iterations) while in C# it comes out to the expected 50% is there some thing different I do not know about java’s Random maybe?

Here is the code:

import java.util.Random;

public class main {


    public static void main(String args[]) {
        Random random = new Random();

        int gamesPlayed = 0;
        int gamesWon = 0;

        for (long i = 0; i < 1000l; i++) {

            int originalPick = random.nextInt(3);
            switch (originalPick) {
            case (0): {
                // Prize is behind door 1 (0)
                // switching will always be available and will always loose
                gamesPlayed++;
            }
            case (1):
            case (2): {
                int hostPick = random.nextInt(2);
                if (hostPick == 0) {
                    // the host picked the prize and the game is not played
                } else {
                    // The host picked the goat we switch and we win
                    gamesWon++;
                    gamesPlayed++;
                }
            }
            }
        }

        System.out.print("you win "+ ((double)gamesWon / (double)gamesPlayed )* 100d+"% of games");//, gamesWon / gamesPlayed);
    }

}

Answer 1

At the very least, you have forgotten to end each case block with a break statement.

So for this:

switch (x)
{
case 0:
    // Code here will execute for x==0 only

case 1:
    // Code here will execute for x==1, *and* x==0, because there was no break statement
    break;

case 2:
    // Code here will execute for x==2 only, because the previous case block ended with a break
}