If Statements

If statements are a basic part of every programming language. The idea is that they allow you to test a condition and then perform an action if the test passed.

Infinite Loops

As we’ve discussed, loops are a powerful control structure designed to allow you to repeat a certain task until whatever you wanted to do is accomplished (all of your numbers are added together, all of your strings are lower case, etc). We are working on a few basic assumptions here:

• The task we are trying to accomplish is finite
• Every iteration brings us closer to the end
• We can know when we are done

This is why every loop has a condition that tells us when we are done with the loop, and why a for loop intrinsically has a counter variable to make it easy to tell where you currently are.

Why is that important?

When you write a computer program it does exactly what the instructions you gave it make it do. Not what you intended for it to do, not what you think the instructions you gave it should do. It does exactly what they say to do. Let’s look at one of my classically obtuse examples.

 

What this programmer probably meant to have happen here was for the loop to repeat until i is ten and then finish. A small, but important, piece is missing: incrementing i. Instead of printing out the number 1 through 9, it will print out 1 infinite times (or rather, until your computer crashes).

The piece of our loop structure that we missed is that every iteration of the loop leaves us where we were before. If any of our loops assumptions are missing or incorrect, we will probably run into an infinite loop like this one. Most often an infinite loop is the result of programmer error.

Why should you care?

Even though I brought up an example here, you will probably make a similar mistake at least a couple times before you really understand infinite loops. However, knowing what they are and why they happen will help you spot them and correct them much more quickly.

Learning Computer Science: Analogies

Computer Science is abstract. It takes theoretical mathematics that are meant to be too pure to ever have an application, and then creates examples of them in cyberspace. What I'm trying to say is: it's hard to understand.

While loops

Anatomy of a for loop

For loop are named because they run for a specific range of values. They are the most useful when you have an array of objects you want to iterate over or a specific set of numbers you want to get through.

Loops Introduction

Ah, loops. A classic topic. If you don't already, you'll learn to love them. Think of a loop as your friend who doesn't mind repeat tasks. Your parents tell you to wash every fork used at dinner one at a time by hand, and just before your next four hours are consumed with dish soap, your friend steps in to help you and take care of that job for you.

Recursion: The Basics

Recursion. Possibly a Computer Scientist's favorite topic. It's a very deep topic and you could easily write a masters or Ph.D. thesis on some of the more complicated recursive