Operations / Calculation in Java

Question

Okay I have got following for loop:

  public static void main(String []args){
        for (int i=2; i<12 ; i=i+2)
        System.out.print(3-i%3);
        System.out.println();
     }

And it is printing out: 12312. In order to understand how it calculates the numbers I have tried to work it out and according to my working it out the first number should be actually 2.

I am pretty sure, I am wrong with my thinking since BlueJ prints out firstly number 1. But why 1? Can someone explain it?

I have written on a piece of paper the way how I understood/work out the calculation and took a picture of it so you can see my working of getting the number 2 and maybe you can point out my mistake.

enter image description here

_"according to my working it out the first number should be actually 2"_ `3-2%3 = ?` (`%` is the modulus operator) — Alexis C., May 01 '14 at 17:52
@ZouZou, feel free and check the picture I have posted, since it shows exactly the way how I calculated, I know I did a mistake, but I don't know what is wrong in my calculation. — Acemi, May 01 '14 at 17:53
@Acemi The first value of i will be 2. Hence the first computation will be 3-2%3. — Alexis C., May 01 '14 at 17:54
@ZouZou, I thought after 2 I have to add another 2 due to i=i+2 ? So it's 4? Or when I should do i=i+2 ? — Acemi, May 01 '14 at 17:56
@Acemi In the first iteration, i = 2. In the second, i = i + 2 = 2+2 = 4. In the third, i = i +2 = 4 + 2 = 6. In the fourth , i = i +2 = 6 +2 = 8.. and so on till i<12. — , May 01 '14 at 18:00
Oh I see...Now I understand it, okay thank you very everyone for the help. Now I have got it! ^^ — Acemi, May 01 '14 at 18:01

score 3 · Answer 1 · answered May 01 '14 at 17:54

according to my working it out the first number should be actually 2.

Check your calculations: 2 % 3 (the remainder after dividing 2 by 3) is 2. 3 - 2 is 1, so the output is correct.

Note that the operations are not performed in the order in which they are written out: % has higher precedence than subtraction, so it is performed before subtraction. It does not matter in this case, but it is an important thing to keep in mind.

score 2 · Accepted Answer · answered May 01 '14 at 18:01

Based on your notes , I think you misunderstood the behavior of for loop.

As per your notes, you substitute i as 4 ( 2+2) in the first iteration.

 for (int i=2; i<12 ; i=i+2)

But , for the first iteration i will be 2

initial value ; condition ; increment/decrements

end of each iteration the third block will execute (increment/decrements) . So for the first iteration i would be 2

and 3-i%3 w would be 3-(2%3) => 3 - 2 => 1 .

For the next iteration i would be i = i+2 => 2 + 2 => 4 then your answer would be 2

yes thank you for the advise, you are write, I kind of misunderstood the way how the for loop was actually calculating. — Acemi, May 01 '14 at 18:03

Operations / Calculation in Java

2 Answers2