Chapter 2: Data Types in C++

A data type specifies the kind of value a variable can store. It also determines:

• How much memory the variable uses
• What range of values it can hold
• What operations can be performed on it

For example:

• An age is stored as an integer.
• A price is stored as a floating-point number.
• A grade is stored as a character.
• A user's login status is stored as a boolean value.

Choosing the correct data type improves performance, memory usage, and code readability.

Why Do We Need Data Types?

Imagine a program that stores different kinds of information:

• Student age → Whole number
• Product price → Decimal number
• User name → Text
• Exam result → True or False

A single data type cannot efficiently represent all of these values. C++ provides different data types for different purposes.

Categories of Data Types

C++ data types can be grouped into three categories:

1. Fundamental (Built-in) Data Types

• int
• float
• double
• char
• bool
• void

2. Derived Data Types

• Arrays
• Pointers
• References
• Functions

3. User-Defined Data Types

• struct
• class
• enum
• union

In this chapter, we'll focus on the most commonly used built-in types.

Integer (int)

The int type stores whole numbers without decimal points.

Syntax

cppCopy
1int age = 21;

Example

cppCopy
1#include <iostream>
2
3using namespace std;
4
5int main()
6{
7    int apples = 10;
8
9    cout << apples;
10
11    return 0;
12}

Output

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110

Common Uses

• Age
• Quantity
• Score
• Year
• Number of students

Floating-Point (float)

The float type stores decimal numbers with single precision.

Syntax

cppCopy
1float price = 99.99f;

The f suffix indicates a float literal.

Example

cppCopy
1#include <iostream>
2
3using namespace std;
4
5int main()
6{
7    float temperature = 36.5f;
8
9    cout << temperature;
10
11    return 0;
12}

Output

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136.5

Common Uses

• Temperature
• Height
• Weight
• Product price

Double (double)

The double type stores decimal numbers with double precision, offering greater accuracy than float.

Syntax

cppCopy
1double pi = 3.14159265358979;

Example

cppCopy
1#include <iostream>
2
3using namespace std;
4
5int main()
6{
7    double salary = 45250.75;
8
9    cout << salary;
10
11    return 0;
12}

Output

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145250.75

float vs double

For scientific calculations and financial applications, double is generally preferred.

Character (char)

The char type stores a single character enclosed in single quotes.

Syntax

cppCopy
1char grade = 'A';

Example

cppCopy
1#include <iostream>
2
3using namespace std;
4
5int main()
6{
7    char letter = 'Z';
8
9    cout << letter;
10
11    return 0;
12}

Output

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1Z

A char stores the character's ASCII (or compatible) code internally.

Boolean (bool)

The bool type stores one of two values:

• true
• false

Syntax

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1bool isLoggedIn = true;

Example

cppCopy
1#include <iostream>
2
3using namespace std;
4
5int main()
6{
7    bool passed = true;
8
9    cout << passed;
10
11    return 0;
12}

Output

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11

By default, true is displayed as 1 and false as 0.

To display the words instead:

cppCopy
1#include <iostream>
2
3using namespace std;
4
5int main()
6{
7    bool passed = true;
8
9    cout << boolalpha << passed;
10
11    return 0;
12}

Output

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1true

String (string)

The string type stores a sequence of characters (text).

To use string, include the <string> header.

Example

cppCopy
1#include <iostream>
2#include <string>
3
4using namespace std;
5
6int main()
7{
8    string name = "Ankit";
9
10    cout << name;
11
12    return 0;
13}

Output

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1Ankit

Common Uses

• Names
• Addresses
• Messages
• Email IDs

Auto (auto)

The auto keyword lets the compiler determine the variable's type automatically based on its initializer.

Example

cppCopy
1auto age = 21;
2auto price = 99.95;
3auto grade = 'A';
4auto name = string("Ankit");

The compiler deduces:

• age → int
• price → double
• grade → char
• name → string

Complete Example

cppCopy
1#include <iostream>
2#include <string>
3
4using namespace std;
5
6int main()
7{
8    auto city = string("Delhi");
9    auto population = 20000000;
10
11    cout << city << endl;
12    cout << population;
13
14    return 0;
15}

The sizeof Operator

The sizeof operator returns the size (in bytes) of a data type or variable.

Example

cppCopy
1#include <iostream>
2
3using namespace std;
4
5int main()
6{
7    cout << sizeof(int) << endl;
8    cout << sizeof(double) << endl;
9    cout << sizeof(char) << endl;
10    cout << sizeof(bool);
11
12    return 0;
13}

Sample Output

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14
28
31
41

The exact sizes may vary depending on your compiler and platform.

Type Conversion

Implicit Conversion

The compiler automatically converts a smaller type to a larger compatible type.

cppCopy
1int marks = 90;
2double score = marks;
3
4cout << score;

Output

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190

Explicit Conversion (Casting)

You can manually convert one type to another.

cppCopy
1double price = 99.95;
2
3int roundedPrice = static_cast<int>(price);
4
5cout << roundedPrice;

Output

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199

Summary of Common Data Types

Best Practices

• Use int for whole numbers.
• Prefer double over float unless memory usage is critical.
• Use bool for logical values.
• Use string for text instead of character arrays.
• Use auto when the type is obvious from the initializer.
• Choose the smallest suitable data type without sacrificing correctness.

Common Beginner Mistakes

Using char for Multiple Characters

Incorrect:

cppCopy
1char name = 'Ankit';

Correct:

cppCopy
1string name = "Ankit";

Forgetting the f Suffix for float

cppCopy
1float price = 99.99f;

Storing Decimal Values in int

Incorrect:

cppCopy
1int value = 12.75;

Correct:

cppCopy
1double value = 12.75;

Practice Exercises

Exercise 1

Create variables of different data types and print them.

cppCopy
1#include <iostream>
2#include <string>
3
4using namespace std;
5
6int main()
7{
8    int age = 22;
9    double salary = 45000.50;
10    char grade = 'A';
11    bool passed = true;
12    string name = "Ankit";
13
14    cout << name << endl;
15    cout << age << endl;
16    cout << salary << endl;
17    cout << grade << endl;
18    cout << boolalpha << passed;
19
20    return 0;
21}

Exercise 2

Print the size of different data types using sizeof.

cppCopy
1#include <iostream>
2
3using namespace std;
4
5int main()
6{
7    cout << "int: " << sizeof(int) << " bytes" << endl;
8    cout << "double: " << sizeof(double) << " bytes" << endl;
9    cout << "char: " << sizeof(char) << " bytes" << endl;
10
11    return 0;
12}

Interview Questions

1. What is a data type in C++?
2. What is the difference between float and double?
3. When should you use bool?
4. What does the auto keyword do?
5. What is the purpose of the sizeof operator?
6. What is implicit type conversion?
7. How is explicit type conversion performed in C++?
8. Why is string preferred over a character array for text?

Summary

In this chapter, you learned:

• What data types are and why they matter.
• How to use int, float, double, char, bool, string, and auto.
• The difference between float and double.
• How to determine memory size with sizeof.
• How implicit and explicit type conversions work.
• Best practices and common mistakes when selecting data types.

In the next chapter, you'll learn Input and Output in C++, including cin, cout, endl, and getline(), allowing your programs to interact with users.