I have a cheat for CI4. To activate the cheat keys, go to options, then gameplay, then click "Allow Cheats.". The keys are:
F5 Adds a new life.
F6 Adds a new missile.
F7 Creates lots of power-ups.
F8 Skip the current wave.
You have to BUY the game in order for these to work, if you don't know the game then go to interactionstudios.com. They have AWESOME games