Why does variable i not change after i=i++?

Question

I didn't understand the below question in LinkedIn's Java Assessment Test:

for(int k =0; k<10; k=k++) {
   k+=1;
   System.out.println("Hello world.");
}

Why does this code print 10 times "Hello world."?

I know k++ means, first do job (calculate,assign,etc.) then increment k. So I think for k=k++, k must be incremented after assignment:

k=k;
k=k+1;

which in the end, I am expecting to get k=k+1.

For example below code prints j=0 and j=1:

int j=0;
System.out.println("j=" + j++);
System.out.println("j=" + j);

Dear java experts, can you explain why k=k++ does not change k?

`a=a++` has 2 steps: 1. evaluation, 2. assignment. The `++` part happens during evaluation, and then gets overwritten by the assignment — Aviad P., Jul 17 '21 at 19:24
Please *USE YOUR DEBUGGER*!!!! Step through the code. Look at the value of each variable at each step. I think you'll see a number of things you probably "don't expect" ;) For example, `k=+1` will assign the value "+1" ;) — paulsm4, Jul 17 '21 at 19:24
Short suggestion: **only use `++` in a standalone expression**. For instance, only do `i++;` and never `i = i++;`. — MC Emperor, Jul 17 '21 at 19:27
Opps. Sorry my fault. It is k+=1; instead of k=+1;. I edited. — Kuvalya, Jul 19 '21 at 23:02

Arvind Kumar Avinash · Accepted Answer · 2021-07-17T22:14:12.297

2

Why does this code print 10 times "Hello world."?

No, this will be an infinite loop because the following statement resets the value of k to 1:

k=+1;

Also, k=k++ will not change the value of k because it is processed something like

int temp = k;
k++;
k = temp;

You can try the following code to verify this:

int k = 1;
k = k++;
System.out.println(k); // Will print 1

edited Jul 17 '21 at 22:14

answered Jul 17 '21 at 19:26

But could you explain why `k=k++` does not change the value of k ? – LetsGoBrandon Jul 17 '21 at 21:57
2

@LorisFoe - I've updated my answer to explain this. Thank you. – Arvind Kumar Avinash Jul 17 '21 at 22:14
@Arvind, sorry its my fault that it is k+=1; – Kuvalya Jul 19 '21 at 23:05
@Kuvalya - No worries. In that case, `k+=1;` will cause the value of `k` to increase in every iteration. I hope, the explanation regarding `k = k++;` is clear to you. Whenever I get enough time, I will also update the answer as per the update of your question. Feel free to comment in case of any further doubt. – Arvind Kumar Avinash Jul 20 '21 at 09:44

score -1 · Answer 2 · answered Jul 17 '21 at 19:26

-1

It should de k+=1

for(int k =0; k<10; k=k++) {
   k+=1;
   System.out.println("Hello world.");
}

If you want to get for k=0 => k=2

  for(int k =0; k<10; k=k+2) {
       System.out.println("Hello world.");
    }

answered Jul 17 '21 at 19:26

Andreea Purta

2 Answers2