C++ Variables and Data Types

A C++ program often needs to store information while it is running. For example, we may need to store a student’s name, age, marks, or a product price.

In C++, we use variables to store this information, while data types tell C++ what kind of information a variable can store. Let’s begin with C++ variables and data types.

What is a Variable?

A variable is a named place used to store a value.

Think of a variable like a box with a name on it. You can put a value inside the box and use it later.

For example:

int age = 14;

Here:

• int is the data type.
• age is the variable name.
• 14 is the value stored in the variable.

Creating a Variable

The basic syntax is:

dataType variableName = value;

For example:

int marks = 85;

You can display the value using cout:

#include <iostream>
using namespace std;

int main() {
    int marks = 85;

    cout << "Marks: " << marks;

    return 0;
}

Output:

Marks: 85

Changing a Variable’s Value

The value of a variable can be changed after it is created.

#include <iostream>
using namespace std;

int main() {
    int age = 14;

    cout << "Age: " << age << "\n";

    age = 15;

    cout << "New Age: " << age;

    return 0;
}

Output:

Age: 14
New Age: 15

What is a Data Type?

A data type tells C++ what kind of value a variable will store.

Some commonly used C++ data types are:

Let’s see some examples.

int

int is used for whole numbers.

int age = 14;
int marks = 90;

float

float is used for decimal numbers.

float height = 5.7;

double

double is also used for decimal numbers and generally provides more precision than float.

double price = 199.99;

char

char stores a single character. The character is written inside single quotes.

char grade = 'A';

bool

bool stores either true or false.

bool passed = true;

string

string is used to store text.

string name = "Rahul";

When using string, include the <string> library:

#include <iostream>
#include <string>
using namespace std;

int main() {
    string name = "Rahul";

    cout << "Name: " << name;

    return 0;
}

Output:

Name: Rahul

Using Different Data Types Together

A program can use different data types at the same time.

#include <iostream>
#include <string>
using namespace std;

int main() {
    string name = "Rahul";
    int age = 14;
    double marks = 88.5;
    char grade = 'A';
    bool passed = true;

    cout << "Name: " << name << "\n";
    cout << "Age: " << age << "\n";
    cout << "Marks: " << marks << "\n";
    cout << "Grade: " << grade << "\n";
    cout << "Passed: " << boolalpha << passed;

    return 0;
}

Output:

Name: Rahul
Age: 14
Marks: 88.5
Grade: A
Passed: true

This is how variables and data types work together to store different kinds of information.

Rules for Naming Variables

C++ has a few simple rules for variable names:

• A variable name can contain letters, numbers, and _.
• It cannot start with a number.
• Spaces are not allowed.
• C++ keywords such as int and return cannot be used as variable names.
• C++ is case-sensitive.

For example:

int studentAge = 14;
int student_age = 14;

Both are valid variable names.

But this is not valid:

int 2age = 14;

A Simple Example

Let’s create a small program that stores a student’s information.

#include <iostream>
#include <string>
using namespace std;

int main() {
    string name = "Anjali";
    int age = 14;
    double marks = 91.5;

    cout << "Name: " << name << "\n";
    cout << "Age: " << age << "\n";
    cout << "Marks: " << marks;

    return 0;
}

Output:

Name: Anjali
Age: 14
Marks: 91.5

Key Points to Remember

• A variable stores information in a program.
• A data type tells C++ what kind of value a variable stores.
• int is used for whole numbers.
• float and double are used for decimal numbers.
• char stores one character.
• bool stores true or false.
• string stores text.
• Variable names should be clear and meaningful.

Mini Quiz

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C++ PROGRAMMING - QUIZ 3

1 / 5

Q1. What is a variable used for in C++?

To store a value

To create comments

To compile a program

To display only text

2 / 5

Q2. Which data type is used to store whole numbers?

char

float

int

bool

3 / 5

Q3. Which data type is used to store a single character?

string

char

double

int

4 / 5

Q4. Which of the following is a valid C++ variable name?

2age

student age

int

student_age

5 / 5

Q5. Which data type stores either true or false?

bool

char

float

string

Your score is

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#include <iostream>
#include <string>
using namespace std;

int main() {
    string productName = "Laptop";
    int quantity = 5;
    double price = 49999.99;
    float rating = 4.5;
    char category = 'E';
    bool available = true;

    cout << "Product: " << productName << "\n";
    cout << "Quantity: " << quantity << "\n";
    cout << "Price: " << price << "\n";
    cout << "Rating: " << rating << "\n";
    cout << "Category: " << category << "\n";
    cout << "Available: " << boolalpha << available;

    return 0;
}

What’s Next?

Now that you know how to store information, the next chapter will show you how to take input from the user and display output in C++ using cin and cout.

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Written by Shubhranshu Shekhar, who has trained 20000+ students in coding.

Nidhi Srivastav