If you take off into Class B or Class C airspace using VFR, are you automatically cleared into it?

In order to get into Chicago you need a mode C transponder which you should already have to be at nashville. but you need to call O'Hare and tell them a 30 min. window of when you will be there and get clearence that way. If you are actually planning to go to O'Hare I wouldnt if I were you. When me and my flight instructor landed there ATC kept telling us to expedite our decent to the point we were landing as fast as we were flying. then we had to slam on the brakes to get the next taxi way to park. not fun.