Commenting Your Code

Now that we know how to structure our program, let's discuss how to style our program. Your code is useless if nobody else can tell what it does. You'd be surprised how fast it even becomes useless to you yourself because you've forgotten what the goal of the program is. To avoid this unfortunate problem, each program you write must first be structured in a logical way. Each small step gets tucked away inside of a function. Then, all of your code must contain comments to more completely describe in English what happens in your program. Naming your functions sensibly goes a long way, but English is often more quickly decipherable.

Commenting Code

Comments are special lines of your program that are not written in code, but in plain English. Comment lines begin with special characters, as shown below

/*  This is a multiline comment.  That
* means that every line that starts with
* a star (astrisk) is a comment. It must
* be ended correctly or it will extend
* forever

// This is a single line comment. It ends here.

Comments are absolutely essential in allowing other people to read and understand your code. At the very least, every single one of your functions should have a comment. If you have a complicated chunk of code, or need to explain the process, then you can (and are encouraged!) to put single line comments inside of your functions. However, you do not need to comment every line of your program.

Preconditions and Postconditions

We said that all of your functions should have comments. What should those comments look like?

Every function comment should contain a few words describing the goal of the function. This can be captured in the precondition and postcondition of your function. The precondition describes what assumptions about the world the function makes and what must be true in the world before the function is done. Postconditions describe the state of the world after the function is called.


  1. Precondition - what is true about the world before the function is called
  2. Postcondition - what is true about the world after the function is called.