Explain the difference between a function prototype and a function definition.?

I don't have access to your book. Doesn't matter.

A function prototype declares (note the use of DECLARE, not DEFINE) the function's name, return type, and the types and number of parameters (unless ... is used.) It does NOT create such a function. It simply declares it so that the compiler knows what to do with such a call.

A function definition creates an instance of code that is the function, as well as declaring it. So a definition does both the work of declaration (prototyping) AND definition (function object creation.)

A prototype may look like:

    int f( int a );

while a definition may look like:

    int f( int a ) { return a; }

The first example doesn't create the function. It simply declares some knowledge about it. The second example both declares knowledge about it AND creates it, as well.

A definition is always also a declaration. But a declaration is not necessarily a definition.

Definition Of Prototype

Prototype Definition