Code Complete, 2nd Edition

Special Considerations in the Use of Functions

Modern languages such as C++, Java, and Visual Basic support both functions and procedures. A function is a routine that returns a value; a procedure is a routine that does not. In C++, all routines are typically called "functions"; however, a function with a void return type is semantically a procedure. The distinction between functions and procedures is as much a semantic distinction as a syntactic one, and semantics should be your guide.

When to Use a Function and When to Use a Procedure

Purists argue that a function should return only one value, just as a mathematical function does. This means that a function would take only input parameters and return its only value through the function itself. ...