Thread: If Then Statement Question!

Okay so here is my code. For my project we have to calculate the monthly payment for a mortgage. My professor wants us to set it up so when someone enters a negative number for any of the inputs it still lets you enter the rest of them but at the end, the program outputs a message that says "ALL NUMERICAL NUMBERS MUST BE POSITIVE!". I understand the if-then-else statements but I just don't know how to make the program JUST send out the message and not do the calculations if the number is negative. Someone please help! (Also, I know the if statement I have is incorrect, I'm just trying to use an example of what I was saying previously and that the prgram outputs a message but still doees the calculations.)

package mortgagecalculation2a;
 
import java.text.NumberFormat;
import java.util.Scanner;
 
/**
 *
 * @author Akira
 */
public class MortgageCalculation2a {
 
    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
 
        Scanner in = new Scanner(System.in);
 
 
        double loanAmount;
        double interestRate;
        double numberYears;
        double months;
        double monthlyPayment;
 
        System.out.print("Enter the loan amount: ");
        loanAmount = Double.parseDouble(in.nextLine());
 
        if (loanAmount < 0) {
            System.out.println("ALL NUMERICAL VALUES MUST BE POSITIVE!");
        }
 
        System.out.print("Enter the rate: ");
        interestRate = Double.parseDouble(in.nextLine());
 
        System.out.print("Enter the number of years: ");
        numberYears = Double.parseDouble(in.nextLine());
 
        interestRate = interestRate / 100 / 12;
 
        months = numberYears * 12;
 
        monthlyPayment = interestRate * loanAmount * (Math.pow(1+interestRate, months))/(Math.pow(1+interestRate, months)-1);
 
 
        NumberFormat defaultFormat = NumberFormat.getCurrencyInstance();
        System.out.println("The monthly payment is: " +defaultFormat.format(monthlyPayment));
 
    }
}

I already checked out that website before posting, that is why I posted. I didn't really see the help in it. It doesn't say anywhere how to do the question I asked.

--- Update ---

How do I make the output say the message without it doing the calculations too. All I want is it to recognize that a input is negative and have the output give the message.

It basically told me what I already know....
It does not for a fact tell me how I can make it so the message only shows up once as the output and doesn't still do the calculation. I know it's all about experiments but when you've been experimenting for about 2 hours you tend to get a little frustrated..

So I what would I put in the else block? Should I put the monthlyPayment equation so that the calculation will not execute then just do a system.out.println of the message? Also, would I have to repeat this process for interestRate and numberYears?

Well I tried putting the equation in there...all i got was a red bar so that didnt work and I dont know what else to put so I asked, sorry.

if (loanAmount < 0){
        }    else if (monthlyPayment = interestRate * loanAmount * (Math.pow(1+interestRate, months))/(Math.pow(1+interestRate, months)-1)){
 
         System.out.println("ALL NUMERICAL VALUES MUST BE POSITIVE!");
 
        }

This is the first thing I tried and there is a red line under the equation and when I hover over it says "incompatible types" and "the assigned value is never used"

Still confused because you said everything you put in the else if block doesn't execute and if loanAmount and the other variables is less than zero I don't want the equation to be executed.

**Remember: whatever you put in the else block will NOT execute if the if statement is evaluated to true** (big hint right there)

This is an if block:
{
System.out.println("Condition is 0"); // the block is between the curly brackets: { and }
}

 if (loanAmount < 0)
        {
 
            System.out.println(monthlyPayment = interestRate * loanAmount * (Math.pow(1+interestRate, months))/(Math.pow(1+interestRate, months)-1));
        }
        else if (interestRate < 0)
        {
            System.out.println(monthlyPayment = interestRate * loanAmount * (Math.pow(1+interestRate, months))/(Math.pow(1+interestRate, months)-1));
        }
        else if (numberYears < 0)
        {
            System.out.println("ALL NUMERICAL VALUES MUST BE POSITIVE!");         
        }
        else 
        {
            System.out.println(monthlyPayment = interestRate * loanAmount * (Math.pow(1+interestRate, months))/(Math.pow(1+interestRate, months)-1));
        }

I tried it for if, else if and else.

rgthdrghdfg.PNG

Did what you said and the equation still calculated

Okay so I tried option 1 and 2 and it still does the calculation at the end. Also, how would I make it so "The monthly payment is: " not even show up, this is what I was trying to do in the beginning, and just put out the error message just once at the very end where it show the monthly payment, that's what my professors looking for.

double loanAmount;
        double interestRate;
        double numberYears;
        double months;
        double monthlyPayment;
 
        System.out.print("Enter the loan amount: ");
        loanAmount = Double.parseDouble(in.nextLine());
 
        System.out.print("Enter the rate: ");
        interestRate = Double.parseDouble(in.nextLine());
 
        System.out.print("Enter the number of years: ");
        numberYears = Double.parseDouble(in.nextLine());
 
        months = numberYears * 12;
 
        if (loanAmount < 0)
        {
            System.out.println("ALL NUMERICAL VALUES MUST BE POSITIVE!");
        }
        else if (interestRate < 0)
        {
            System.out.println("ALL NUMERICAL VALUES MUST BE POSITIVE!");
        }
        else if (numberYears < 0)
        {
            System.out.println("ALL NUMERICAL VALUES MUST BE POSITIVE!");
        }
        else 
        {
            System.out.println(monthlyPayment = interestRate * loanAmount * (Math.pow(1+interestRate, months))/(Math.pow(1+interestRate, months)-1));
        }
 
        interestRate = interestRate / 100 / 12;
 
        monthlyPayment = interestRate * loanAmount * (Math.pow(1+interestRate, months))/(Math.pow(1+interestRate, months)-1);
 
 
        NumberFormat defaultFormat = NumberFormat.getCurrencyInstance();
        System.out.println("The monthly payment is: " +defaultFormat.format(monthlyPayment));

54354354.PNG
Please look at it, I honestly have no clue what else to do (also, you can't see it but there is a yellow line under the equation saying that the assigned value is never used)

  if (loanAmount < 0)
        {
            System.out.println("ALL NUMERICAL VALUES MUST BE POSITIVE!");
        }
        else if (interestRate < 0)
        {
            System.out.println("ALL NUMERICAL VALUES MUST BE POSITIVE!");
        }
        else if (numberYears < 0)
        {
            System.out.println("ALL NUMERICAL VALUES MUST BE POSITIVE!");
        }
        else  
        {  
        interestRate = interestRate / 100 / 12;
 
        monthlyPayment = interestRate * loanAmount * (Math.pow(1+interestRate, months))/(Math.pow(1+interestRate, months)-1);
 
        NumberFormat defaultFormat = NumberFormat.getCurrencyInstance();
        System.out.println("The monthly payment is: " +defaultFormat.format(monthlyPayment));
        }

ewdgfsdgsdg.PNG

-_-

That didn't work.

package mortgagecalculation2a;
 
import java.text.NumberFormat;
import java.util.Scanner;
 
/**
 *
 * @author Akira
 */
public class MortgageCalculation2a {
 
    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
 
 
        Scanner in = new Scanner(System.in);
 
 
        double loanAmount;
        double interestRate;
        double numberYears;
        double months;
        double monthlyPayment;
 
 
 
        System.out.print("Enter the loan amount: ");
        loanAmount = Double.parseDouble(in.nextLine());
 
        System.out.print("Enter the rate: ");
        interestRate = Double.parseDouble(in.nextLine());
 
        System.out.print("Enter the number of years: ");
        numberYears = Double.parseDouble(in.nextLine());
 
        months = numberYears * 12;
 
      if (loanAmount < 0 || interestRate < 0 || numberYears < 0)
{
	System.out.println("ALL NUMERICAL VALUES MUST BE POSITIVE!");
 
}
else 
{
	interestRate = interestRate / 100 / 12;
 
        monthlyPayment = interestRate * loanAmount * (Math.pow(1+interestRate, months))/(Math.pow(1+interestRate, months)-1);
 
        NumberFormat defaultFormat = NumberFormat.getCurrencyInstance();
        System.out.println("The monthly payment is: " +defaultFormat.format(monthlyPayment));
    System.out.println(monthlyPayment = interestRate * loanAmount * (Math.pow(1+interestRate, months))/(Math.pow(1+interestRate, months)-1));
}
 
        }
 
 
 
    }

This is my goal for what it should look like..
wefdsfgsedfg.PNG