虽然环境仍在继续，但环路仍在继续

Question

Hey everyone so I've been trying to write what should be a really easy counting program for my CS class, but for some reason it keeps spitting back out the "Please enter a number (0 to stop): " prompt and seems to completely disregard the while loop. If the condition inside the while loop is being met, why does the while loop not stop even if 0 is entered? I have done C# in the past, but I'm not really familiar with Java's caveats, so if there's anything weird that Java doesn't like me to do let me know. For a more detailed description of the program, it's supposed to read both negative and positive numbers from the user, output the sum of the negatives and the positives individually, and then take the average. (Obviously below is just the problematic piece of code.)

 Scanner scanner = new Scanner(System.in);
    double average;
    double numPositive=0.0;
    double numNegative=0.0;
    double input = 0.0;
    do 
    {
        System.out.print("Please enter a number (0 to stop): ");
            input = scanner.nextDouble();   
        if (input < 0.0)
        {
            numNegative += scanner.nextDouble();

        }
        else if (input > 0.0)
        {
            numPositive += scanner.nextDouble();

        }

    } while (Math.abs(input) > 1.0e-6);  // make the tolerance whatever you want.

Answer 1

You never change input after the initial assignment; the loop will continue on forever. I think you forgot to call scanner.nextDouble() again.

Answer 2

You're not taking in input after initially retrieving it.

Your scanner.nextDouble() assigns to numNegative and numPositive - neither of which is checked by the while loop.

while (input != 0.0)
    {
        System.out.print("Please enter a number (0 to stop): ");
        input = scanner.nextDouble();

        if (input < 0.0)
        {
            numNegative += input;

        }
        else if (input > 0.0)
        {
            numPositive += input;

        }

    }

Answer 3

You are not assigning a value to input anywhere inside your loop. So, the initial value remains, and the loop won't exit.