As you step through the do loop, when you get to the expression j-- < 7, remember (or save) the current value of j, decrement j, then use the saved value of j to

test j < 7. When you get to the expression i++ < 7, remember (or save) the current value of i, increment i, then use the saved value of i to test i < 7.

Here is the first time through the loop:

evaluate 9 < 4

decrement j to 8 before evaluating 9 < 7

increment i to 1

increment i to 2 before evaluating 1 < 7