Compared the displacement with the same time step,
If the displacement is the same, it is moving in constant velocity.
If the displacement is changing, it is accelerating!

I have put those pictures together. Please check out the following picture to find out the answer.
[img]http://www.phy.ntnu.edu.tw/ntnujava/index.php?action=dlattach;topic=1176.0;attach=1462;image[/img]