Why won't my Java while loop stop and let me program terminate?

Question

import java.util.*;

public class Investment 
{

    public static int years=0;
    public static void main(String[] args) 
    {
        Scanner kbd = new Scanner(System.in);
        System.out.println("Please enter an integer representing the whole dollar value of your initial investment: $");
        int startBal=kbd.nextInt();
        System.out.println("Please enter the whole number percentage, excluding the percent sign, of the interest rate on the investment.");
        int interestRate=kbd.nextInt()/100;
        int endBal=startBal*2;
        int currentBal=startBal;
        while (endBal>=currentBal)
        {
            currentBal=currentBal*interestRate+currentBal;
            years++;
        }
        System.out.println("It will take "+years+" years to double your investment.");
    }
}

The output I'm seeing is:

Please enter an integer representing the whole dollar value of your initial investment: $
10000
Please enter the whole number percentage, excluding the percent sign, of the interest rate on the investment.
5

The "10000" and "5" are my input. The program should be printing my final statement with the answer "15," but instead doesn't do anything, and doesn't terminate.

This is a good question. Code is there. Input, expected output, and actual output are all there. — But I'm Not A Wrapper Class
– But I'm Not A Wrapper Class, Commented Oct 16, 2014 at 17:36
Please don't edit in "solved" to your title. Here in SO, you can "accept" exactly one answer that solved your problem by clicking the checkmark next to that answer. — rgettman
– rgettman, Commented Oct 16, 2014 at 17:56

AntonH · Accepted Answer · 2014-10-16 17:35:25Z

3

int interestRate=kbd.nextInt()/100;

Since interestRate is an int, it gets rounded down to zero.

So this line:

currentBal=currentBal*interestRate+currentBal;

resolves to:

=> currentBal=currentBal*0+currentBal;
=> currentBal=0+currentBal;
=> currentBal=currentBal;

So the value never increases, so will never reach double its initial value, so infinite loop.

You would have to replace the line with:

double interestRate=kbd.nextInt()/100.0;

answered Oct 16, 2014 at 17:35

AntonH

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1 Comment

AntonH Over a year ago

@Squidicide No problem :) Instead of editing title as "Solved - ...", accept an answer, and it will appear different on the Questions page.

VAndrei · Accepted Answer · 2014-10-16 17:35:42Z

1

Your interestRate is declared as an int so it will be set to 0.

You should declare all values as doubles, since we-re talking about money we want to be precise :)

answered Oct 16, 2014 at 17:35

VAndrei

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Comments

Community · Accepted Answer · 2017-05-23 12:20:28Z

1

You have an int interest rate, which when divided by 100, becomes 0. Make it a double and use the double literal 100.0 to divide, to force floating-point division.

double interestRate=kbd.nextInt()/100.0;

The currentVal variable will need to be a double also.

My output with the changes:

Please enter an integer representing the whole dollar value of your initial investment: $
10000
Please enter the whole number percentage, excluding the percent sign, of the interest rate on the investment.
5
It will take 15 years to double your investment.

This will let the program finish. But normally it's not a good idea to use a double to store money.

edited May 23, 2017 at 12:20

CommunityBot

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answered Oct 16, 2014 at 17:36

rgettman

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Comments

brso05 · Accepted Answer · 2014-10-16 17:37:19Z

0

Your doing integer division 5/100 which = 0 remainder 5. So in your calculation you are multiplying by 0 so your current balance will always be 0 and never reach end balance. Try using a double for your interest rate rather than an integer.

answered Oct 16, 2014 at 17:37

brso05

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Comments

tviana · Accepted Answer · 2014-10-16 17:38:54Z

0

while (endBal>=currentBal)
{
    currentBal=currentBal*interestRate+currentBal;
    years++;
}

of course it never terminate, you are only incrementing years but the variables on the while are endBal and currentBal

answered Oct 16, 2014 at 17:38

tviana

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1 Comment

Amitesh Rai Over a year ago

However, the currentBal is being continuously modified while iterating, Isn't it ? and infinite looping is because of the user dividing 5/100, which is always going to be 0, and hence the interestRate and as a consequence the currentBal also.

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