Warning: Control reaches end of non-void function

Warning: Control reaches end of non-void function--Reason and Solution

  The reason for this warning is that the compiler thinks your function may never return something at the end of the function, though you are 100% sure that it can return what you expect.

 The solution is simple, just add a statement returning something at the end of you function body. And the warning or error will disappear.

UPDATE!

 Last time I said that the solution the the problem is to add a expression "return 0;" to the end of the function. However, when I was having class, our teacher gave us a better solution! That is: REMOVE THE ELSE SENTENCE !  If the condition is satisfied, the following expression will be executed and an  integer will be returned. If the condition is not satisfied, directly return a -1 and the function is ended. Here is the demonstration:

This way is succinct and more logical. But it seems it can't be applied in the first example.