Question

I am having trouble understanding the following code block.

   int count = 0;
   for (int i = 0; i < 3; i++){
       count += (count++);
       System.out.println("count = " + count);
       System.out.println("i = " + i);
   }

My understanding is that the loop runs three times preforming the following

count = count + count
count = 1 + count

This translates to the following as count initially is 0:

count = 0 + 0
count = 1 + 0 = 1
count = 1 + 1 = 2
count = 1 + 2 = 3
count = 3 + 3 = 6
count = 6 + 1 = 7

The output is below, and count is printed as 0.

    count = 0
    i = 0
    count = 0
    i = 1
    count = 0
    i = 2

Could someone explain this to me?
Thanks

Answer 1

count += (count++);

is equivalent to

in tmp = count;      // right hand side of +=
count = count + 1;   // the count++
count = tmp + tmp;   // executing count += tmp

As you can see the count = count + 1 has no effect, since the value of count is overwritten in the last line, and if count is initially 0, then the result will obviously be count = 0 + 0 🙂