Loops in simple Java program

Question

I'm working on a program for my Java class which needs to calculate how many children a couple would need to have in order to have one of each sex, assuming its a 50/50 chance that the child will be a male. The program then needs to keep track of how many times it took 2 children to have one of each sex, how many times it took 3 children, 4 children, and finally 5 or more children in T amount of trials. I tackled this by nesting a while loop within a for loop that runs T amount of times. My problem is that, although my for loop is running T amount of times, my while loop will spit out, say, 3 children and then not update for the rest of the for loop. Any advice as to how to get the while loop to update properly? Thanks!

public class B
{
    public static void main(String[] args) 
    {
        int girls = 0;
        int boys = 0;
        System.out.print("Enter variable: ");
        int T = StdIn.readInt();

        for (int i = 0; i < T; i++)
        {
            while ((boys < 1) || (girls < 1))
            {
                if (Math.random() < 0.5)
                {
                    boys = boys + 1;
                }   
                else
                {
                    girls = girls + 1;
                }   
            }
        }
    }
}

Your code is doing exactly what you asked it to do. I fear that you don't understand the problem statement correctly. — duffymo
– duffymo, Commented Sep 9, 2015 at 0:43

Jason · Accepted Answer · 2015-09-09 01:31:44Z

3

You need to reset the boy and girl count each run. Therefore the code around your while loop should be:

boys = 0;
girls = 0;
while ((boys < 1) || (girls < 1))

But then after the while loop, you need to calculate which family size this run applies to: 2 kids, 3 kids, 4 kids, 5+ kids and increment the appropriate counter.

switch(boys + girls) {
    case 2:
        twoKids++;
    break;

    case 3:
        threeKids++;
    break;

    case 4:
        fourKids++;
    break;

    default:
        fivePlusKids++;
}

edited Sep 9, 2015 at 1:31

answered Sep 9, 2015 at 0:47

Jason

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6 Comments

glac19 Over a year ago

Thats what I was thinking too, but running my program with && rather than || does not produce the proper output. If I run the program outside of the for loop and add in some code to print out how many boys and girls there are, it works correctly with || and produces things like girls: 0 boys: 2 with &&. I just need a way to make my while loop repeat so that i get, say, 10 separate outpost from it.

Jason Over a year ago

You're right - the problem isn't in the while clause, it is because you needed to reset the count of boys and girls. I've edited the answer.

Hunter McMillen Over a year ago

What if you want to track families with 10+ kids? The switch case solution doesn't seem to scale for that. An array seems more appropriate.

Jason Over a year ago

The OP never requested that. But it could be done by storing the result in a map keyed by the number of children. An array would not scale well either.

Hunter McMillen Over a year ago

@Jason One array to maintain state seems preferable to N counters. Initialize the array to the number of children you want to track and each element represents the count for N kids.

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