Inch  cm conversion program
The first point would be the separation of concerns: every entity (function, class …) should only be responsible for one task (except, ironically, printing the result).

In your code, one function (conversion) is responsible for everything. Try separating the different issues:


user input
conversion
output


Granted, for such a very small program the result will almost certainly be larger. But it will also be much clearer and easier to extend.

Next up, your use of recursion. I love recursion as much (more!) as the next programmer but in your case a few loops wouldn’t hurt readability.

A third point, magic constants should be avoided. Your use of the conversion factors 2.2 and 1.45 is innocuous enough but it soon becomes a problem in larger programs. Use properly-named constants instead.