C++

Basics

Boilerplate

#include <iostream>using namespace std; int main() {    cout << "Welcome To CodeWithHarry";    return 0;}

Input/Output

• Output (cout <<) – Prints to console
• Input (cin >>) – Takes user input

string name;cout << "Enter name: ";cin >> name;cout << "Hello, " << name;

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Data Types

C++ supports several data types, divided into categories:

Type	Example	Size (Typical)	Description
char	char c='A';	1 byte	Stores single character
int	int x=10;	4 bytes	Integer numbers
short	short s=100;	2 bytes	Small integer
long	long l=100000;	4-8 bytes	Large integer
float	float f=10.5;	4 bytes	Single-precision decimal
double	double d=10.55;	8 bytes	Double-precision decimal
bool	bool flag=true;	1 byte	True/False values
void	–	–	Represents no value

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Escape Sequences

Sequence	Meaning
\a	Alert (beep)
\b	Backspace
\f	Form feed
\n	Newline
\r	Carriage return
\t	Horizontal tab
\\	Backslash
\'	Single quote
\"	Double quote
\?	Question mark
\0	Null terminator
\nnn	Octal value
\xhh	Hexadecimal value

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Comments

// Single-line comment /* Multi-line   comment */

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Strings

#include <string> string s1 = "Hello";string s2 = "World"; // Concatenationstring s3 = s1 + " " + s2; // Appends1.append(s2); // Lengthcout << s3.length(); // Access/modifys3[0] = 'h';

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Math Functions (<cmath>)

Function	Example	Result
max(a,b)	max(5,10)	10
min(a,b)	min(5,10)	5
sqrt(x)	sqrt(144)	12
ceil(x)	ceil(1.9)	2
floor(x)	floor(1.9)	1
pow(x,y)	pow(2,3)	8
abs(x)	abs(-5)	5
round(x)	round(2.6)	3

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Decision Making

if (x > 0) { ... }else if (x == 0) { ... }else { ... } // Ternaryint result = (x > 0) ? 1 : -1; // Switchswitch (choice) {    case 1: cout << "One"; break;    case 2: cout << "Two"; break;    default: cout << "Other";}

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Loops

// While loopwhile (i < 5) { i++; } // Do-while loopdo { i++; } while (i < 5); // For loopfor (int i=0; i<5; i++) { ... } // Break/Continuebreak;     // exits loopcontinue;  // skips current iteration

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References

int a = 10;int &ref = a;ref = 20; // a becomes 20

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Pointers

int x = 10;int *ptr = &x;   // Pointer to xcout << *ptr;    // Dereference (prints 10)

• nullptr is used for null pointers in C++11+
• Use -> operator to access members of objects through pointers

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Functions & Recursion

int add(int a, int b) {    return a + b;} // Recursionint factorial(int n) {    if (n <= 1) return 1;    return n * factorial(n-1);}

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Object-Oriented Programming

Class & Object

class Car {public:    string brand;    int year;    void drive() { cout << "Driving"; }}; Car c1;c1.brand = "BMW";c1.drive();

Constructor

class Car {public:    Car(string b, int y) {        brand = b;        year = y;    }    string brand;    int year;};Car c("Audi", 2023);

Inheritance

class Vehicle {public:    void honk() { cout << "Beep!"; }}; class Car : public Vehicle { }; Car obj;obj.honk(); // Inherited method

Polymorphism (Virtual Functions)

class Animal { public: virtual void sound() { cout<<"Some sound"; }};class Dog : public Animal { public: void sound() override { cout<<"Bark"; }};Animal* a = new Dog();a->sound(); // Bark

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File Handling

#include <fstream>ofstream myFile("test.txt");  // writemyFile << "Hello";myFile.close(); ifstream readFile("test.txt");  // readstring line;while (getline(readFile, line)) { cout << line; }readFile.close();

• Modes: ios::in, ios::out, ios::app, ios::binary, ios::ate, ios::trunc

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Exception Handling

try {    throw runtime_error("Error occurred");}catch (exception &e) {    cout << "Caught: " << e.what();}

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Additional Key Concepts

• Namespaces: Avoids name conflicts

namespace A { int x = 10; }cout << A::x;

• Templates: Generic programming

template <typename T>T add(T a, T b) { return a + b; }

• STL (Standard Template Library): vector, map, set, stack, etc.