Thread: Programming Exercise Help

 
/*
Chapter 3 Debugging Assignment
Programmer: Nicolas
Date: 18 February 2014
Program Name: bert.java
Purpose:
*/
 
import java.util.Scanner;
 
public class bert
{
    public static void main(String[] args)
    { 
        //Declaring Variables
        int price, downPayment, tradeIn, months;
 	double annualInterest;
        String custName;
 
        Scanner reader = new Scanner (System.in);
 
        //Get Input from User
        System.out.println("What is your first name? ");
        custName = reader.next();
        System.out.print("What is the price of the car? ");
        price = reader.nextInt();
        System.out.print("What is the downpayment? ");
        downPayment = reader.nextInt();
        System.out.print("What is the trade-in value? ");
        tradeIn = reader.nextInt();
        System.out.print("For how many months is the loan? ");
        months = reader.nextInt();
        System.out.print("What is the decimal interest rate? ");
        annualInterest = reader.nextDouble();
 
        //Output
calculatePayment (price, downPayment, tradeIn, annualInterest, months, custName);
    }
 
    public static void calculatePayment(int price, int downPayment, int tradeIn,
            double annualInterest, int months, String custName)
    {
        int interest;
        double loanAmt;
 	double payment;
 
	//Calculations
interest = (int)annualInterest / 12;
loanAmt = price-downPayment-tradeIn;
 
 
payment = ((1/interest)-(1/(interest*Math.pow(1+interest,months))))/loanAmt;
 
 
	System.out.print("The monthly payment for " + custName + " is $");
	System.out.println(payment);
 
    }
}

So far all I can gather is it is a problem with the equation and zero. Farther than that I am lost and I just can't seem to figure the rest out. It's the last error I need to fix.

Help is much appreciated.

My bad, the error that appeared when compiled and run is:
"Exception in thread "main" java.lang.ArithmeticException: / by zero
at bert.calculatePayment(bert.java:53)
at bert.main(bert.java:38)
Java Result: 1
BUILD SUCCESSFUL (total time: 5 seconds)"

payment = ((1/interest)-(1/(interest*Math.pow(1+interest,months))))/loanAmt;

That is line 53. It refers back to

interest = (int) ((double)annualInterest / 12);
loanAmt = price-downPayment-tradeIn;

1 is being divided by interest, and I'm assuming that interest is being equal to 0.

I know that interest is appearing as 0.

The interest rate I need is determined by the annual interest in decimal form presented earlier (in first code) instituted into the second code.

System.out.print("What is the decimal interest rate? ");
        annualInterest = reader.nextDouble();

interest = (int) ((double)annualInterest / 12);

The inputs I used art the following which includes error, shown in output.

run:
What is your first name? 
Ames
What is the price of the car? 17500
What is the downpayment? 500
What is the trade-in value? 1250
For how many months is the loan? 60
What is the decimal interest rate? .05
Exception in thread "main" java.lang.ArithmeticException: / by zero
	at bert.calculatePayment(bert.java:52)
	at bert.main(bert.java:38)
Java Result: 1
BUILD SUCCESSFUL (total time: 25 seconds)

When you cast a floating point number (float or double) to an integer it will always round down to the next whole number. If your annual interest is 0.05 and you calculate your interest like this:

interest = (int) ((double)annualInterest / 12);

then the result will inevitably be 0.
So either your calculation function is wrong or your input is not acceptable.

Originally Posted by Cornix

When you cast a floating point number (float or double) to an integer it will always round down to the next whole number. If your annual interest is 0.05 and you calculate your interest like this:

interest = (int) ((double)annualInterest / 12);

then the result will inevitably be 0.
So either your calculation function is wrong or your input is not acceptable.

That is basically the point of the exercise. It's a debugging exercise and I can't figure out how to fix this one completely.

The calculation is where the problem is I believe. You actually answered the same type of question once, where I think the problem was the same..

http://www.javaprogrammingforums.com...ning-code.html

run:
What is your first name? 
Ames
What is the price of the car? 17500
What is the downpayment? 500
What is the trade-in value? 1250
For how many months is the loan? 60
What is the decimal interest rate? .05
Exception in thread "main" java.lang.ArithmeticException: / by zero
	at bert.calculatePayment(bert.java:52)
	at bert.main(bert.java:38)
Java Result: 1
BUILD SUCCESSFUL (total time: 25 seconds)

I'm kind of confused because the calculations don't occur due to error. I believe you helped answer approx. the same problem where I'm still confused.

http://www.javaprogrammingforums.com...ning-code.html

We are trying to find the payment you have to make. Interest is suppose to be determined by the annual interest already presented in the questions divided by 12.

For annual interest 0.05, which is then divided by 12 or something for interest I think.

Your telling me.. It's a debugging exercise trying to determine the payment by doing some equation in the code. Interest is suppose to come from the input you give, I usually put 0.05 when you run the program and you start with the question inputs.

Interest is annual interest / 12 is it not?

Oh, 0.004 is expected. I'm getting the error and when I println the problem it shows interest as a 0. Why the difference is what I can't figure out. Not sure why it's getting a 0.