Variables

What is a Variable?

A variable has a name, and you can store something in it.

The image below shows how we can think of a variable named favFruit, with the value 'apple' stored inside it.

Below is how we can create the favFruit variable, using Python code:

The code above creates a variable named favFruit, and the equal sign = is used to store the value 'apple' inside the variable.

The reason for giving a variable a name is to be able to use it later in the code, and also to know what value it holds.

Creating a Variable

Below is the code for creating the favAnimal variable in different programming languages.

favAnimal = 'turtles'

const favAnimal = 'turtles';

String favAnimal = "turtles";

const string fav_animal = "turtles";

Variables can hold different types of data, like whole numbers, decimal numbers, or text.

Doing Things with Variables

Like we have just seen in the previous example, a value can be stored in a variable. And if you run the example code above, you see how a variable is printed.

We can do other things with variables as well, like math operations, or put variables with text strings together.

Add a Variable to a String

To use a variable in a string, you can add it to the string, like this:

a = 'Jane'
print('Hello, my name is ' + a)

const a = 'Jane';
console.log('Hello, my name is ' + a);

String a = "Jane";
System.out.println("Hello, my name is " + a);

string a = "Jane";
cout << "Hello, my name is " + a;

Add Two String Variables Together

You can add two string variables together to form a sentence, using the + operator, like this:

a = 'Jane'
b = 'My name is '
print(b + a)

const a = 'Jane';
const b = 'My name is ';
console.log(b + a);

String a = "Jane";
String b = "My name is ";
System.out.println(b + a);

string a = "Jane";
string b = "My name is ";
cout << b + a;

Add Two Number Variables

If the variables are numeric values, you can perform mathematic operations on them, like adding two numbers:

a = 2
b = 3
print(a + b)

const a = 2;
const b = 3;
console.log(a + b);

int a = 2;
int b = 3;
System.out.println(a + b);

int a = 2;
int b = 3;
cout << to_string(a + b) + "\n";

or other mathematical operations, like division:

a = 12
b = 3
print(a / b)

const a = 12;
const b = 3;
console.log(a / b);

int a = 12;
int b = 3;
System.out.println(a / b);

int a = 12;
int b = 3;
cout << to_string(a / b) + "\n";

Another way to add two variables, is to make an extra variable c to hold the sum, and present the answer with a text string:

a = 2
b = 3
c = a + b
print('The sum a + b is ' + str(c))
 
 

const a = 2;
const b = 3;
const c = a + b;
console.log('The sum a + b is ' + c);
 
 

int a = 2;
int b = 3;
int c = a + b;
System.out.println("The sum a + b is " + c);
 
 

int a = 2;
int b = 3;
int c = a + b;
cout << "The sum a + b is " + to_string(c) + "\n";
 
 

Incrementing a Variable

We can create a variable, and update the value by adding 1 to it, like this:

a = 2
a = a + 1
print(a)

let a = 2;
a = a + 1;
console.log(a);

int a = 2;
a = a + 1;
System.out.println(a);

int a = 2;
a = a + 1;
cout << a;

Incrementing a variable is a common operation in programming, and it's often used in loops. It is so common in fact, that many programming languages have a shorthand for it, like ++ in C/C++ and Java, or += in Python.

The code below shows how to increment a variable in different programming languages, using shorthand.

a = 2
a += 1
print(a)

let a = 2;
a++;
console.log(a);

int a = 2;
a++;
System.out.println(a);

int a = 2;
a++;
cout << a;

Decrementing a Variable

If we want to decrement a variable, we can do that in a similar way as incrementing. And the number we want to decrement by can be any number, not just 1.

The code below shows how to decrement a variable by 3 in different programming languages, using shorthand.

a = 5
a -= 3
print(a)

let a = 5;
a -= 3;
console.log(a);

int a = 5;
a -= 3;
System.out.println(a);

int a = 5;
a -= 3;
cout << a;

Using a Variable in an if Statement

We can use a variable in an if statement, as part of the condition, like this:

temperature = 25
print('Temperature: ' + str(temperature) + '°C')

if temperature > 20:
  print('It is warm')
else:
  print('It is not warm')

const temperature = 25;
console.log('Temperature: ' + temperature + '°C');

if (temperature > 20) {
  console.log('It is warm');
} else {
  console.log('It is not warm');
}

int temperature = 25;
System.out.println("Temperature: " + temperature + "°C");

if (temperature > 20) {
  System.out.println("It is warm");
} else {
  System.out.println("It is not warm");
}

int temperature = 25;
cout << "Temperature: " + to_string(temperature) + "°C\n";

if (temperature > 20) {
  cout << "It is warm\n";
} else {
  cout << "It is not warm\n";
}

The Variable Name

There are certain rules that applies when naming a variable. Some rules are programming-languange-specific, other applies to all programming languages:

• A variable name cannot contain spaces.
• A variable name cannot start with a number.
• A variable name cannot be a reserved word like if, else, for, function etc.

For readability, it is common to use camelCase or snake_case when naming variables, so instead of myfavanimal, we can use myFavAnimal or my_fav_animal.