Computer Programming: How Variables work 

Easy computer programming tutorial for beginners on working with variables.


What is a ‘Variable’ in computer programming?

Image a box.

Let’s name this box, “Toy Box”. This box is special because it’s made of oak wood and holds Jimmy’s favorite toy nerf-guns.


A variable is just that. It is a box that holds something important; information — more specifically a value.

Just like a wooden ‘Toy Box’ that holds some nerf guns. A variable is a box that has a type, a name and a some thing [a value] it stores.

Note: A variable can be used to hold something different later on in the program. For example, Jimmy can decide to hold another toy in his ‘Toy Box’ instead of nerf-guns when ever he wants to.

What is the purpose of a variable: Let’s say I want to create a really cool game called Tetris, and want to save the highest score achieved by a player.

I can use a variable to hold the highest score scored in the game.

Type of a variable

Although you can give your variable box any name you want, the value it can hold can only be of a certain type.

The type of information — value — e.g. numbers, letters, answers etc. your variable can hold depends on the type of variable box it is.

Type of value must equal the type of variable

Like a wooden “toy box” in the real world, a variable box can be one of several types — mainly the 8 primitive data types.

But for now you only need to know the 3 of 8 data types.

  1. Int —A variables of data type int can hold whole integers.
  2. char — A variable of data type char can hold a single character.
  3. double — A variable of data type double can hold decimal value integer.

Naming a variable

Of course you can give it any kind of name you want, however, it is good code practice to begin the name [of a variable] with only the first letter written in small letters.

For example: I can declare a variable of type int and give it a name: “evenNumber” or “oddNumber” or just “number”.
int evenNumber;
float oddNumber;
char letter;

Notice the first letter of the the word ‘even’ is in small letters and the first letter of the second word is capitalized.

It is a good habit write clean code with proper programming conventions as you’re learning how to program.

Finally, how to use a variable in an actual program.

A) You must declare the variable

Declaring a variable simply means to define it by giving it a name and a type.

You have just learnt this. Here is another example:

Int wholeNumbers;

Where: Int is the Type and ‘wholeNumbers is name of the variable.

B. Next you must assign a value you want the variable to hold

Assigning a value to a variable is done through ‘assignment statements’.

This is easy.

Assignment statement is a statement for assigning a value that your variable needs to hold e.g. like a set of nerf-guns.

Note: The first time you assign a value to a variable, it is called initializing the variable. We use this terminology because the value of the variable was null when you initially declared it. But now that you gave it a value through an assignment statement, you have initialized the variable for the first time!

You can assign a value to a variable using the ‘=’ operator.

Here’s an example:

int evenNumber; //Declaring [define] a variable
evenNumber = 2; // initializing [assigning] a value

The variable type is int so it can only store whole integers. Name of the variable is evenNumber and the ‘=’ operator expresses the value given to the variable which is 2.

QUIZ TIME

Let’s see what you have learnt so far. Use the comments section to submit your answers!

  1. Declare a variable of type int and give it name ‘age’, and assign your age to it.
  2. Declare a variable of type char and assign it the value of the 9th letter of the alphabet.
  3. Declare a variable and assign it with the highest score of 13.5 in a game of Tetris.

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