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.

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.

Frequently Asked Questions (FAQs)

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

Nidhi Srivastav