Question

why am I getting the following output: 4 8 12 16 20

int i, j = 1, k;
  for (i = 0; i < 5; i++)
  {
     k = j++ + ++j;
     Console.Write(k + " ");
  }

Answer 1

I don’t think the other answers here are correct.

The variables are evaluated in order according to mathematical ordering operations. In this case, we are just adding, so they are evaluated left to right. j++ and then ++j

j++ + ++j

1. j       let’s call the value of j at the start of the loop p
2. j++   j evaluates to the pre-increment value (p) and then j is incremented (p+1)
3. ++j   j is incremented (p+2) and evaluates as the post-increment value (p+2)

So, the two evaluated numbers are p + p+2:

i  initial j  j++ + ++j   k   j
================================
0      1       1  +  3    4   3
1      3       3  +  5    8   5
2      5       5  +  7   12   7
3      7       7  +  9   16   9
4      9       9  + 11   20  11