This is definitively a nice start for a beginner but as a Python developer with some experience, I would like to give you some quick suggestions to make your code better:

• You should never declare functions inside loops. This is very inefficient as the program is declaring the same code over and over, which slows the code and may waste additional memory space.

• You should not access the global variables in the body of the function. This is considered a bad design as modifying their values inside the function may break the program. Instead, you should declare the needed variables as function parameters then call the functions with values of those global variables.

• if c=='y' or c=='Y': can be simplified to if c.lower() == 'y':.

That's what I have noticed until now, I hope that will help you in the future.