Java - While loop will not exit

Question

//Loop that isn't working. I keep pressing a number that is 1,2,3,4, or 5 but it won't exit the loop. The operator seems to be assigned the value that I input but it still will not exit the while loop. I'm trying to write a basic calculator with simple math operations but this turned into a very annoying problem.

import java.util.Scanner;
public class BasicCalculatorTwo {
    public static void main(String[] args){
        Scanner scanner = new Scanner(System.in);
        int operator;
        double fnum, snum, answer;
        operator = 0;

        System.out.println("Enter first number : ");
        fnum = scanner.nextDouble();
        System.out.println("Enter second number : ");
        snum = scanner.nextDouble();

        while(operator != 1 || operator != 2 || operator != 3 || operator != 4 || operator != 5 ){
            System.out.println();
            System.out.println(fnum + " ? " + snum + " = ");
            System.out.println("1 : Add");
            System.out.println("2 : Subtract");
            System.out.println("3 : Multiply");
            System.out.println("4 : Divide");
            System.out.println("5 : Modularize");
            operator = scanner.nextInt();
        }

        switch(operator){
            case 1:
                answer = fnum + snum;
                break;
            case 2:
                answer = fnum - snum;
                break;
            case 3:
                answer = fnum * snum;
                break;
            case 4:
                answer = fnum / snum;
                break;
            case 5:
                answer = fnum % snum;
                break;
            default:
                break;
            System.out.println(fnum + " ? " + snum + " = " + answer);
            scanner.close();
        }
    }
}

The while loop condition is always true. The operator variable is always either not 1 or not 2 -- think of this logically and you'll see. You want to use && not ||. — Hovercraft Full Of Eels
– Hovercraft Full Of Eels, Commented Sep 29, 2015 at 2:09
operator != 1 OR operator != 2 OR operator != 3 OR operator != 4 OR operator != 5 - this will always be true. Maybe you meant to use == or &&? Anytime you have an infinite loop, look at your control expression and your control variable. — mkobit
– mkobit, Commented Sep 29, 2015 at 2:12
Oh, i literally just read the while loop to myself out loud and now I see why it is stuck in an infinite loop. — ArcticJag
– ArcticJag, Commented Sep 29, 2015 at 2:17

GubiD · Accepted Answer · 2015-09-29 02:31:52Z

2

You loop conditional is the problem.

while (operator != 1 || operator != 2 || operator != 3 || operator != 4 || operator != 5)

It should be

while (operator != 1 && operator != 2 && operator != 3 && operator != 4 && operator != 5)

Basically, you're saying that if the operator is != 1, then do the loop. Likewise each of the others. If you were to utilize && operators instead of || it would work much better.

Really, what you want to say is that operator is > 1 && < 5, then loop, otherwise break.

while(operator < 1 || operator > 5)
{
  DoPrintStuffHere();
}

Think about it logically, you want any number less than 1 OR greater than 5 to loop again.

edited Sep 29, 2015 at 2:31

answered Sep 29, 2015 at 2:17

GubiD

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3 Comments

ArcticJag Over a year ago

When i add the "while(operator < 1 && operator > 5)" the while loop doesn't run.

GubiD Over a year ago

Oops, yeah, I did the same thing you did. This is always false. You cannot be always < 1 && > 5. In this case, you would utilize the or operator ||

Mousey Over a year ago

@Hovercraft full of eels gave the same answer in a comment

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