Variables

A variable is a named box in memory where your program keeps a value, like a name, an age or a price.

Creating a Variable

Imagine a label on a jar in a kitchen: the label is the variable's name, and what is inside is its value.

In Python you just write the name, an equals sign =, and the value:

student = "Ali"
age = 17
print(student)
print(age)

Ali
17

In JavaScript you start with the word let:

let student = "Ali";
let age = 17;
console.log(student);
console.log(age);

Ali
17

The = sign does not mean "equals" like in maths. It means "put this value into this box".

Changing a Variable

The value in a variable can change. That is why it is called a *variable*.

price = 300
print(price)
price = 350
print(price)

300
350

let price = 300;
console.log(price);
price = 350;
console.log(price);

300
350

In JavaScript you use let only the first time. After that, you just use the name.

Types of Values

Values come in different kinds, called data types. The most common ones are:

Notice that Python writes True with a capital T, while JavaScript writes true in lowercase.

Using Variables Together

Variables become useful when you combine them. Here a small shop in Karachi works out a bill:

item = "Notebook"
price = 120
quantity = 3
total = price * quantity
print(item, "total: Rs", total)

Notebook total: Rs 360

let item = "Notebook";
let price = 120;
let quantity = 3;
let total = price * quantity;
console.log(item, "total: Rs", total);

Notebook total: Rs 360

Both print() and console.log() can show several values at once if you separate them with commas. They put a space between each value.

Joining Text

You can join strings with +. In Python, a number must be turned into text first with str():

name = "Ayesha"
marks = 88
print("Student: " + name + ", marks: " + str(marks))

Student: Ayesha, marks: 88

let name = "Ayesha";
let marks = 88;
console.log("Student: " + name + ", marks: " + marks);

Student: Ayesha, marks: 88

JavaScript turns the number into text for you automatically.

Naming Rules

Good names make code easy to read. Follow these rules in both languages:

• Names can use letters, digits and the underscore _
• A name cannot start with a digit (2price is not allowed)
• No spaces: write total_price (Python style) or totalPrice (JavaScript style)
• Names are case sensitive: Age and age are two different variables
• Choose names that describe the value: fee is better than x

Exercise