It always seems like when I play one coin in the slots, that's when I hit the jackpot, and when I play three coins I get nothing. Are the machines programmed to do that?
No, your experience has just been coincidence. The combinations you see on the reels are determined by a computer program called a "random number generator." It continually generates random numbers corresponding to potential reel combinations. It works away even when no one is playing.
When you hit the button and signal the machine that you're about to play, the random number generator stops on a number and sets the reel combination for that spin.
The random number generator does not communicate with the machine's coin-counting mechanism. The programs are on separate chips, so the random number generator does not know how many coins you've played. If your timing in playing maximum coins was the same as your timing in playing one coin, you would see the same combination on the reels.
