As for crypt() there might be another file you need to include, since the function is not defined anywhere within your program. The warnings can be ignored for now, but if the program does not run as expected look over.

The 'assignment makes pointer wihtout a cast' is a warning regarding the lack of a descriptor to indicate type conversion. Some compilers take care of this upon compilation, but the warning is still given as to indicate that the code might not be cross-compatible [some compilers might execute the code differently from what is expected].

Does the book specify on what platform the code is meant to be run on, or is it ANSI standardized? If it is the latter then everything's fine, however if not you should be carefull about includes. <stdio.h> isn't a required include in Linux using gcc but Windows compilers always required it [as far as I've used them].

Anyway I hope this helps... again, check for an include for the crypt() function.