A program is always working with information. The information, or data, that a program needs is kept somewhere in a computer’s memory. Memory in a computer is arranged so that the data stored there can be found using an address. An address is a number that tells where the data that program wants to use is located in memory.

For a program, using an address number to get and store data is very inconvenient. So, programs use variables instead. A variable represents the place in memory for the data that’s kept there. It’s called a variable because the data it represents may change (vary) when the program stores something new there. When you create a new variable in your program, you’re reserving a place in memory for some data that your program might want to create, copy, or check on later.

Variables have a name, a type, and a value:

  • name - how you’ll refer to the variable
  • type - the kind of data a variable will store
  • value - what’s stored (the data) in the variable

You can use the default variable names given in the blocks if you’d like. However, it’s best to use descriptive variable names. To change a variable name in the editor, select the down arrow next to the variable and then click “Rename variable…”.

let statement

Use the Block Editor variable statement to create a variable and the assignment operator to store something in the variable. This is called declaring the variable.

For example, this code stores the number 2 in the x variable:

let x = 2;

Here’s how to make a variable in the Block Editor:

  1. Click variables.

  2. Change the default variable name if you like.

  3. Drag a block type on the right-side of the assignment operator and click the down arrow to change the variable name.

When you make, or declare, a variable in code, you’ll use the let statement. It looks like this:

let percent = 50;

Reading variable values

Once you’ve declared a variable, just use the variable’s name whenever you need what’s stored in the variable.

let count = 10
let half = count / 2

Updating variable values

To change the contents of a variable use the assignment operator.

let count = 10
if (count < 20) {
    count = 20

Why use variables?

If you want to remember and modify data somewhere in your program later, you’ll need a variable.

Local variables

Local variables exist only within the function or block of code where they’re declared.

Here, the variable index only exists inside the for block. The looping variable exists both outside and inside the for block.

let looping = true;
for (let index = 0; index <= 10; index++) {
    if (index == 10) {
        looping = false;

See also

Assignment operator, Change operator