pxt-calliope/docs/courses/csintro/variables/overview.md

Introduction

Computer programs process information. Some of the information that is input, stored, and used in a computer program has a value that is constant, meaning it does not change throughout the course of the program. An example of a constant in math is ‘pi’ because ‘pi’ has one value that never changes. Other pieces of information have values that vary or change during the running of a program. Programmers create variables to hold the value of information that may change. In a game program, a variable may be created to hold the player’s current score, since that value would change (hopefully!) during the course of the game.

Ask the students to think of some pieces of information in their daily life that are constants and others that are variables.

• What pieces of information have values that don’t change during the course of a single day (constants)?
• What pieces of information have values that do change during the course of a single day (variables) Constants and variables can be numbers and/or text.

Examples

In one school day...

• Constants: The day of the week, the year, student’s name, the school’s address
• Variables: The temperature/weather, the current time, the current class, whether they are standing or sitting...

Variables hold a specific type of information. The micro:bit's variables can keep track of numbers, strings, booleans, and sprites. The first time you use a variable, its type is assigned to match whatever it is holding. From that point forward, you can only change the value of that variable to another value of that same type.

• A number variable could hold numerical data such as the year, the temperature, or the degree of acceleration.
• A string variable holds a string of alphanumeric characters such as a person's name, a password, or the day of the week.
• A boolean variable has only two values: true or false. You might have certain things that happen only when the variable called gameOver is false, for example.
• A sprite is a special variable that represents a single dot on the screen and holds two separate values for the row and column the dot is currently in.