Variables and Constants

Variables and constants are basic building blocks of C++ programming. They are used to store data that a program can use and process.

What is a Variable?

A variable is a named memory location used to store data. The value of a variable can change during program execution.

Syntax of Variable

data_type variable_name;

Example:

int age;

Initializing a Variable

You can assign a value to a variable during declaration.

int age = 18;

Example Program

#include <iostream>
using namespace std;

int main() {
    int age = 18;

    cout << age;

    return 0;
}

Output

18

Types of Variables

Integer Variable

Stores whole numbers.

int number = 10;

Float Variable

Stores decimal numbers.

float price = 99.5;

Character Variable

Stores single characters.

char grade = 'A';

String Variable

Stores text.

string name = "Ali";

Rules for Naming Variables

• Names can contain letters, digits, and underscore
• Names cannot start with a number
• Spaces are not allowed
• C++ keywords cannot be used
• Variable names are case-sensitive

Valid examples:

int age;
float total_marks;

Invalid examples:

int 2age;
float total marks;

What is a Constant?

A constant is a value that cannot be changed during program execution.

Using const Keyword

const float PI = 3.14;

Example of Constant

#include <iostream>
using namespace std;

int main() {
    const int DAYS = 7;

    cout << DAYS;

    return 0;
}

Output

7

Difference Between Variable and Constant

Variable	Constant
Value can change	Value cannot change
Declared normally	Declared using const
Used for changing data	Used for fixed values

Why Variables and Constants are Important

They are important because they:

• Store program data
• Help perform calculations
• Make programs flexible
• Improve code readability
• Manage fixed and changing values efficiently

Real-Life Example

• Variable → Bank balance that changes
• Constant → Number of days in a week

Conclusion

Variables and constants are essential concepts in C++ programming. Variables store changing data, while constants store fixed values. Understanding them helps build a strong foundation for programming and problem-solving.