Why does this self addition equal 0?

Question

Curious about how fast self addition would grow, I wrote a quick little loop in Java to see:

int count = 1;
while(true){
    System.out.println(count);
    count += count;
}

The output was unexpected:

0
0
0
0
0
...

Why is this? count is initialized to 1, so the inner addition should be doing count + count or 1 + 1. Why is the result 0?

Answer 1

The output you've posted is the trailing lines of the output, not the first 30-31 lines. It goes so fast that after the first 31 iterations it goes beyond INT MAX and the addition results in 0. Remember that a signed integer has a max value of 2^31, or 4 bytes with a sign bit.

Instead of while(true) { try while(count>0) {, you will get to see the first few iterations when it wasn't 0.