Okay... here is the 80 lives cheat code for the original Super Contra nintendo game:

You enter this at an opening screen before the game starts i think.. it's pretty obvious..

Up-Down-Up-Down-Left-Left-Right-Right--A-B-A-B- (select) - Start

The select changes to 2 player mode.. leave it out for one player.

You may say that 80 is not infinite. The game lets you continue after your initial lives are lost 3 or 4 times. It still does this in 80 life mode. We did some experiments and proved that with two players, after teaching any small child or anyone with opposable thumbs really, to press the fire and forward buttons, you can't lose with this many lives.