Bubble sort complexity
There is just one loop in for, so the number of steps here will be proportional to n not n^2. The outer loop is running in a n proportional number of steps too. So The complexity of your algorithm is n^2.
N.B. : When speaking complexity, you don't have to state (n^2 + n) / 2,just say n^2 because they are the same for big ns.