Lesson 11: Introduction to loops

If you recall the lesson on colors, you'll remember that we ended up creating a big block of mostly repetitive code. There is a better way to accomplish what we did there and that's using loops. This lesson will be a brief introduction to loops, but future lessons will build upon it and teach you how to write the color palette program without much repetition.

While loops

Let's start with a simple form of looping: while loops. Take a look at the following example:

The following diagram explains how that bit of code works:

As you can see from the diagram, the program starts with a variable n that has been initialized to 0. We start the loop by checking the value of n. Everything inside the while loop is indented once (has the same amount of whitespace before it). The contents of the loop are usually called the "body" of the loop. The body of this loop makes sure that n is incremented by 1. The body also has a "side-effect" of printing the value of n. And that's how we end up with 5 print statements. When n finally becomes 5, it no longer passes the n < 5 check and the loop exits. Finally, the last line of the program runs as expected.

Note that we start looping at n = 0 and never print out n as 5. This is a very common pattern in computer science (starting at 0). This will be an especially important pattern in Code the blocks, since the 3D plane we're operating in is centered around the coordinates 0, 0, 0.

Combining inputs with loops

The source-pane below has been populated with a partial example that combines inputs with the loops that you just learnt about. The purpose of this piece of code is to accept a number from the user between 0 and 10 and place that many cubes. See if you can finish the piece of code.

You'll notice things like int() and str() in the code. Don't worry about them for now. We'll go over "types" in a future lesson.

In the next lesson, I'll reveal the solution and go over it.