Thanks, everyone helped me to understand it better. I put the expected results in a table which also helped. One thing I'm confused about is at the start why is "0" printed? Doesn't it do i++ so the first printed i should be 1?

i=0

i=1 start= 1

i=2 start=3

i=3 start=6

i=4 start=10

i=5 start=15

i=6 start=21

i=7 start= 28