Introduction

When you use an app, you’re almost always changing something—for example, the score in a game, the text in a message, or the number of photos in your photo album.

In this lesson, you’ll learn how to create values that can change as your program runs. Changeable values allow you to build programs that can adjust to the shifting nature of real-life situations. You’ll also learn why it might be important to create values that will never change.

Go Build

Open the "Constants and Variables.playground" file in the folder you downloaded and follow the instructions.

Screenshot of the Variables playground

Reflection Questions

Look around the room you’re in. Can you divide the things in the room into constants and variables? If you were in the same room tomorrow, or next week, what things would be the same and what will have changed?

Think of the rules of a sport or game. During the course of the game, what remains constant and what varies? Would the game be better if anything about it could change at any time, or do the constants make it a better game?

Think of an app you use and all of the information it holds to do its job. Can you divide the information into variables and constants?

Summary

Introducing variables makes your code more exciting and powerful, but it can also make unexpected things happen if you aren't careful.

Constants and variables are both useful tools, and it’s important to know when and where to use each one. You’ve started to think about how a program models a real-life situation, which aspects of that situation can change, and which should stay the same.