rounding down (this is helpful because we' rather have little extra space in each row than an overly crowded row nextset up loop that counts from to the number of aliens we need to make in the main body of the loopcreate new alien and then set its -coordinate value to place it in the row each alien is pushed to the right one alien width from the left margin nextwe multiply the alien width by to account for the space each alien takes upincluding the empty space to its rightand we multiply this amount by the alien' position in the row then we add each new alien to the group aliens when you run alien invasionyou should see the first row of aliens appearas in figure - figure - the first row of aliens the first row is offset to the leftwhich is actually good for gameplay because we want the fleet to move right until it hits the edge of the screenthen drop down bitthen move leftand so forth like the classic game space invadersthis movement is more interesting than having the fleet drop straight down we'll continue this motion until all aliens are shot down or until an alien hits the ship or the bottom of the screen note depending on the screen width you've chosenthe alignment of the first row of aliens may look slightly different on your system