3 replies to this topic

[Cruel Hand]

I've made a fahrenheit to celsius conversion table with the following source code:

public class HelloWorld {

	public static void main(String[] args) {

		System.out.println("Far-Cel Converter");

		

		int lower, upper, step;

		double far, cel;

		

		lower = 0;

		upper = 300;

		step = 20;

		

		far = lower;

		while (far <= upper){

			cel = (far - 32.0) * 5.0/9.0;

			Math.round(far);

			Math.round(cel);

			System.out.print(far);

			System.out.println("-");

			System.out.println(cel);

			far = far + step;

		}

	}

}

once I initialize the value of variable cel, I call on the math.round method to round the value of cel to the nearest number, but it doesn't for some reason. Does anyone know why?

Thanks :)

[Directive]

Even though you called round on far and cel, you did not update the variables, so when you call print you still get the values before round was called.

If you add an assignment, the problem is fixed.

public class HelloWorld {

	public static void main(String[] args) {


		System.out.println("Far-Cel Converter");

	

		int lower, upper, step;

		double far, cel;

		

		lower = 0;

		upper = 300;

		step = 20;

		

		far = lower;

		while (far <= upper) {

			cel = (far - 32.0) * 5.0/9.0;

                        //update variables

			far =  Math.round(far);

			cel = Math.round(cel);

			System.out.print(far);

			System.out.println("-");

			System.out.println(cel);

			far = far + step;

		}

	}

}

[Cruel Hand]

ahh ok, thanks! I didn't know that I had to initialize the new value of cel in order to get the return value from math.round.

i get it now, thanks a lot :)

[wim DC]

Strings and primitives (byte, int, double, float, boolean etc. - anything starting with a small letter) will never 'magically' change value like that, just because they can't. A new initialization will always be required.

More classes require this kind of initialization all the time, but in theory they could have done without.
Like:

BigInteger integer = new BigInteger("11");

integer = integer.add(new BigInteger("2"));

In this case you also have to do it, but the Java programmers could have actually done it without needing to do it.
I think they just wanted you to give the option to keep the original value.


Note that if you have something like:

far = lower;

while (far <= upper) {

    ......

    far = far + step;

}

You can replace it by:

for(far = lower ; far<=upper ; far += step){

    ......

}