Data Types and Variables in C++

What are Data Types in C++?

Data types specify the type of data a variable can hold. Each data type has a specific size and range, which defines the type of values it can store.

Why Data Types are Important:

• They help optimize memory usage.
• They ensure type safety, preventing invalid operations.
• They define how data is interpreted by the compiler.

Categories of Data Types in C++

1. Primitive (Built-in) Data Types: Directly supported by C++.
2. Derived Data Types: Formed using built-in types.
3. User-Defined Data Types: Custom data types created by the programmer.

Primitive (Built-in) Data Types

These are the basic data types provided by C++.

Example:

#include <iostream>
using namespace std;

int main() {
    int age = 25;
    float height = 5.8f;
    double weight = 72.5;
    char grade = 'A';
    bool isStudent = true;

    cout << "Age: " << age << endl;
    cout << "Height: " << height << " feet" << endl;
    cout << "Weight: " << weight << " kg" << endl;
    cout << "Grade: " << grade << endl;
    cout << "Is Student: " << isStudent << endl;

    return 0;
}

Output:

Age: 25
Height: 5.8 feet
Weight: 72.5 kg
Grade: A
Is Student: 1

Derived Data Types

These are data types derived from primitive types.

1. Arrays: Collection of elements of the same type.

int numbers[5] = {1, 2, 3, 4, 5};

2. Pointers: Variables that store the memory address of another variable.

int x = 10;
int *ptr = &x;

3. References: An alias for another variable.

int y = 20;
int &ref = y;

4. Function Types: Return and parameter types of functions.

int add(int a, int b) {
    return a + b;
}

User-Defined Data Types

These allow you to create your own custom types.

1. Structures (struct)

struct Student {
    string name;
    int age;
    char grade;
};

2. Unions (union)

union Data {
    int intValue;
    float floatValue;
};

3. Enumerations (enum)

enum Color {RED, GREEN, BLUE};

4. Classes (class) (Advanced - Covered in OOP Chapter)

class Car {
public:
    string brand;
    int year;
};

What are Variables in C++?

Variables are containers for storing data. They are named storage locations in memory.

Declaring Variables

• Syntax:

data_type variable_name;

• Example:

int age;
float height;
char grade;

Initializing Variables

Variables can be assigned a value at the time of declaration.

int age = 25;
float height = 5.9;
char grade = 'A';

Types of Variable Initialization

1. Direct Initialization:

int number = 10;

2. Copy Initialization:

int number(10);

3. Uniform Initialization (C++11):

int number{10};

Multiple Variable Declaration

int a = 5, b = 10, c = 15;

Scope of Variables

The scope defines where a variable can be accessed.

1. Local Variables: Declared inside functions or blocks.

void display() {
    int x = 10;  // Local variable
}

2. Global Variables: Declared outside any function.

int count = 0;  // Global variable

void increment() {
    count++;
}

3. Static Variables: Retain their value between function calls.

void demo() {
    static int num = 0;
    num++;
    cout << num << endl;
}

Example:

#include <iostream>
using namespace std;

int globalVar = 100; // Global variable

void display() {
    int localVar = 50; // Local variable
    static int staticVar = 0; // Static variable
    staticVar++;
    cout << "Local Variable: " << localVar << endl;
    cout << "Static Variable: " << staticVar << endl;
    cout << "Global Variable: " << globalVar << endl;
}

int main() {
    display();
    display();
    return 0;
}

Output:

Local Variable: 50
Static Variable: 1
Global Variable: 100
Local Variable: 50
Static Variable: 2
Global Variable: 100

Constants in C++

Constants are variables whose value cannot change during program execution.

Defining Constants:

1. Using const Keyword:

const float PI = 3.14159;

2. Using #define (Preprocessor Directive):

#define MAX_SIZE 100

Difference between const and #define:

• const is type-safe, while #define is not.
• const follows scope rules, while #define is global.

Type Modifiers

Type modifiers allow you to adjust the properties of a data type.

Example:

#include <iostream>
using namespace std;

int main() {
    unsigned int u = 4294967295;
    signed int s = -2147483648;
    short int sh = 32767;
    long int l = 9223372036854775807;
    
    cout << "Unsigned Int: " << u << endl;
    cout << "Signed Int: " << s << endl;
    cout << "Short Int: " << sh << endl;
    cout << "Long Int: " << l << endl;
    return 0;
}

Summary

In this tutorial, you learned:

• What data types and variables are.
• Different categories of data types (Primitive, Derived, User-Defined).
• How to declare, initialize, and use variables.
• The concept of constants and type modifiers.