Building Games in Flash 5 - Part 3 - Enemies and collisions - Page 5

What is a for loop?

For loops are used when you want to repeat some code a set number of times. For loops use a counter, in our case its called i, which is typically increased by one each time flash goes through the loop.

The line for (i=2; i<=numEnemy; i++){ is actually doing quite a lot.
The i=2 bit sets a variable called i equal to 2 when the loop starts. The i++ bit tells flash to increase i by one everytime the loop is repeated and the i<=numEnemy bit tells flash to keep looping while i is less than or equal to numEnemy. So it will stop looping when i is greater than numEnemy.

The result of this is that two duplicates of enemy1 will be created, called enemy2 and enemy3. If you increase the value of numEnemy then the number of duplicate enemies will increase accordingly.

Now, close the actions window and on the main time line add an extra frame to each of the layers (as shown). Select the second frame of the control layer and insert a keyframe (press F6). Open up the actions window for this frame (either Window > Actions or right-click and pick actions) and type the following line:

stop();

This just stops the main timeline.

You might wonder how the game plays if the main timeline is stopped? Well, even though the main timeline is stopped the laser, spaceship and ground movieclips are still playing. The timelines of movieclips run independent of the main timeline, they will only stop if you specifically tell each one of them to stop.

You might also be wondering about why we used the control layer.
We could have just put the code in any one of the other four layers. However its much better practice to include all frame code in a separate layer. This makes it much easier to debug your flash file and for other people to understand your flash file. It also means that if you delete a layer to remove a graphic you wont accidentally also remove some code. It has become a standard in the flash programming community to call this layer control.

If you test your flash file now you should have three enemy spaceships flying across the screen.