Java: Can you explain me the output?

[Hip]

Hey guys,

 

can you explain me why the output is "1" when I input for a = "9" and b = "7"?

 

import javax.swing.*;

public class Calculate
{

	public static void main(String[] args)
	{
		
		String inputA, inputB;
		int a, b;
		
	
		inputA = JOptionPane.showInputDialog(null, "a: ");
		inputB = JOptionPane.showInputDialog(null, "b: ");
	
		
		a = Integer.parseInt(inputA);
		b = Integer.parseInt(inputB);
		
		
		while(a > 0 && b > 0)
		{
			if(a > b)
			{
				a = a - b;
			}
			
			else
			{
				b = b - a;
			}
		}
		
		if(b == 0)
		{
			JOptionPane.showMessageDialog(null, "a : " + a);
		}
		
		else
		{
			JOptionPane.showMessageDialog(null, "b: " + b);
		}

		System.exit(0);
	}
}

 

Thank you in advance!

[MrMG]

Because that is what your algorithm does?

What output are you expecting here? And what are you trying to calculate with this program?

[Hip]

Just now, MrMG said:

Because that is what your algorithm does?

What output are you expecting here? And what are you trying to calculate with this program?

I coded it with a Nassi Schneidermann Diagram I got from university. And the code is 1:1 like the solution by the prof. 

I was expecting the output to be "2". Because when I put in "9" and "7" the first if loop calculates 9 - 7 = a. Shouldn't a be "2" then? But it still goes into the second if loop where b == 0, but why is b == 0 here? I thought it's "7" because I input it before to be "7". This is the part I don't understand.

[MrMG]

7 minutes ago, Hip said:

I coded it with a Nassi Schneidermann Diagram I got from university. And the code is 1:1 like the solution by the prof. 

I was expecting the output to be "2". Because when I put in "9" and "7" the first if loop calculates 9 - 7 = a. Shouldn't a be "2" then? But it still goes into the second if loop where b == 0, but why is b == 0 here? I thought it's "7" because I input it before to be "7". This is the part I don't understand.

Well yes, the first time it goes through the loop a becomes 2. But now a is 2 and b is 7. Both are bigger than 0 so the loop executes a second time. Here is your loop condition:

while(a > 0 && b > 0)

Now b is bigger than a so the else block gets executed which calculates b = b - a; which makes b equal 5. But a = 2 and b = 5 so the loop gets executed another time, now a = 2 and b = 3 . Now it gets executed another time a = 2 b = 1. Now a is bigger than b so a = a - b; which means now a = 1 and then b = 1 and both are still bigger than 0 so we execute the code in the while block another time which calculates b = b - a; which leads to a = 1 and b = 0. Now b is NOT bigger than 0 so the while loop ends and we go to the following if statement:

if(b == 0)
		{
			JOptionPane.showMessageDialog(null, "a : " + a);
		}
		
		else
		{
			JOptionPane.showMessageDialog(null, "b: " + b);
		}

because b == 0 the message dialog shows you the value of a, which is 1.

 

I think you might be forgetting about the while loop, and that's what's confusing you.