How to fix Cracked iPhone 4 screen

I want to buy some iphone 4's (not 4s) that have a cracked screen and I want to buy the parts and fix them myself( I'm a teen and I really want to start fixing iphones and make a profit but I have never bought one from someone else and bought the right parts.) what would be a good price to buy one at that has a cracked screen and how much would the screen and everything it needs to work again cost? Are there any problems that could occur while fixing it? What is the difference from the LCD and digitizer and the glass? Thanks!

Added (1). Also what other smart phones can I buy and fix for a little bit of money and then make a decent profit?

You don't.

You can go to radio shack to get it fixed or get a kit in eBay.

Learn how to to install a screen yourself here: http://www.ifixit.com/...nt/11755/1

About the parts, buy it off eBay from the China guys. Really cheap but you gotta be a little bit patient cause it will take over the course of 3 weeks to arrive. If your in no rush, perfect deal.

The LCD/digitizer is the actually thing that broadcasts you the color. The glass part is the section that covers up your LCD from the elements. The glass is also the thing that senses where your fingers touch so it sends it signal to your iPhone. You can't work a iPhone without a glass.