MarkT:
Unfortunately warnings are disabled in the Arduino compiler
More like "disabled by default". If you go to File->Preferences and check the box for compilation next to Show verbose output during: then hit verify you get the following compiler output:
Blink.ino: In function 'String test(char, int, String)':
Blink.ino:32: warning: control reaches end of non-void function
(presumably because it confuses newcomers to programming)world.
I like to think that it protects those of us who like to help from programmers and newcomers who might have O.C.D. 