Why would you want to create a function? There are several different reasons why you want to have a function:

• You may need a particular functionality for your code that you want to develop in independence of the rest of the code. If you put such a functionality in a function, that means that after developing and testing the functionality you can use it without thinking about it anymore.

• You may need a particular functionality that returns in different places in your code, and rather than copy it to all these places, you write a function for it which you call in all these places.

• You may need a particular functionality in your code that you need to control using parameters. If you put it in a function, the parameters become clearer and the code becomes more readable and easy to maintain.

• Your program may just be getting too long to keep a solid grasp on its contents, and you feel you can improve readability and maintainability by splitting off inherently connected blocks into functions.

• You may have problems solving a big problem in one go, and decide to divide it into sub-problems (which is usually a good idea). You can now create a function for each of these sub-problems, and by connecting them together, solve the big problem.

• Your program may contain deeply nested conditions or loops, and would benefit enormously as far as readability is concerned by moving some of the deeper nestings into functions.

• You may want to re-use code in different programs, and functions are a good way to transfer code between programs.

• You may want to release some of your code to other programmers, and functions are, again, a good way to do that.

In general, the advantage of functions is that they provide a means to effectuate:

• Encapsulation: Wrapping up a piece of useful code in such a way that it can be used without knowledge of the specifics

• Generalization: Making a piece of code useful for a variety of circumstances by controlling it via parameters

• Manageability: Dividing a complex program into easy-to-manage chunks

• Maintainability: Using meaningful names and logical wrappings to make a program better readable and understandable

• Reusability: Facilitating the transfer of functionalities between programs

• Recursion: Allowing the use of a technique called “recursion,” which is the topic of Chapter 10¹.