Variables and Data Types

Table of Contents

No.	Topic
1	Variables
2	Data Types

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Definition of Variables

A variable is like a container used to store data such as numbers, text, or other values in a program. It allows you to use and change that data later by referring to the variable’s name.

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C++

Syntax

<datatype> <variableName> = <value>;

Common data types: int, string (from <string>), double, bool, char

Note: To use string, include the <string> header and use the std namespace.

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Example

#include <iostream>
#include <string>  // Required for using std::string

int main() {
    int age = 25;
    std::string name = "Alice";
    bool isStudent = true;

    std::cout << name << " is " << age << " years old." << std::endl;
    return 0;
}

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C#

Syntax

<datatype> <variableName> = <value>;

Common data types: int, string, double, bool

Example

int age = 25;
string name = "Alice";
bool isStudent = true;

Console.WriteLine(name + " is " + age + " years old.");

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Java

Syntax

<datatype> <variableName> = <value>;

Common data types: int, String, double, boolean

Example

int age = 25;
String name = "Alice";
boolean isStudent = true;

System.out.println(name + " is " + age + " years old.");

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Python

Syntax

variable_name = value

• No need to declare type — Python figures it out automatically

Example

age = 25
name = "Alice"
is_student = True

print(name + " is " + str(age) + " years old.")

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JavaScript

Syntax

let variableName = value;
const variableName = value; // for constants
var variableName = value;   // older way

Example

let age = 25;
let name = "Alice";
let isStudent = true;

console.log(name + " is " + age + " years old.");

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TypeScript

Syntax

In TypeScript, variables can be declared using let, const, or var with type annotations.

let variableName: type = value;
const constantName: type = value;
var oldStyleVariable: type = value;

Example

let age: number = 25;
let name: string = "Alice";
let isStudent: boolean = true;

console.log(`${name} is ${age} years old.`);

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Definition of Data Types

Data types define what kind of value a variable can store, such as numbers, text, true/false, etc. Each programming language has built-in data types used to store specific kinds of data.

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C++

Common Data Types:

• int – whole numbers (e.g., 10)
• double – decimal numbers (e.g., 10.5)
• std::string – text (e.g., "Hello") (requires <string> header)
• bool – true/false values
• char – single character (e.g., 'A')

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Example

#include <iostream>
#include <string>  // Required for std::string

int main() {
    int age = 30;
    double height = 5.9;
    std::string name = "Alice";
    bool isStudent = true;
    char grade = 'A';

    std::cout << name << " is " << age << " years old, height is " << height << " feet." << std::endl;
    std::cout << "Student status: " << (isStudent ? "Yes" : "No") << ", Grade: " << grade << std::endl;

    return 0;
}

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C#

Common Data Types:

• int – whole numbers (e.g., 10)
• double – decimal numbers (e.g., 10.5)
• string – text (e.g., "Hello")
• bool – true/false values
• char – single character (e.g., 'A')

Example

int age = 30;
double height = 5.9;
string name = "Alice";
bool isStudent = true;
char grade = 'A';

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Java

Common Data Types:

• int – whole numbers
• double – decimal numbers
• String – text
• boolean – true/false
• char – single character

Example

int age = 30;
double height = 5.9;
String name = "Alice";
boolean isStudent = true;
char grade = 'A';

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Python

Common Data Types:

• int – whole numbers
• float – decimal numbers
• str – text
• bool – true/false (True or False)
• list, dict, tuple – for collections

Python is dynamically typed — no need to declare type.

Example

age = 30
height = 5.9
name = "Alice"
is_student = True
grade = 'A'

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JavaScript

Common Data Types:

• Number – for all numbers (both integer and decimal)
• String – text
• Boolean – true/false
• Object – for key-value pairs
• Array – list of items
• null – empty value
• undefined – not assigned

Example

let age = 30;
let height = 5.9;
let name = "Alice";
let isStudent = true;
let grade = 'A';

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TypeScript

Common Data Types:

TypeScript builds on JavaScript by adding static type definitions. Below are the most commonly used data types in TypeScript:

Type	Example	Description
string	"Hello, World!"	Textual data
number	42, 3.14	Both integers and floating-point numbers
boolean	true, false	Logical values
null	null	Absence of any value
undefined	undefined	A variable not assigned a value
any	any	Disables type checking
void	function greet(): void {}	Function that does not return a value
never	function error(): never {}	Represents unreachable code or errors
object	{ name: "Alice", age: 30 }	Non-primitive values
array	string[], Array<number>	Ordered collections
tuple	[string, number]	Fixed-length array with known types
enum	enum Color {Red, Green, Blue}	Named constants
union	`string	number`
literal	"yes", 42	Specific value as type
type / interface	type User = {name: string}	Custom structured types

Tip: Use type and interface to define reusable and complex data structures.

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Type Safety is the key feature of TypeScript—leverage these data types to write robust code.

Example

let age: number = 30;
let height: number = 5.9;
let name: string = "Alice";
let isStudent: boolean = true;
let grade: string = 'A'; // TypeScript does not have a 'char' type, use string with 1 character

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