C++ Cheatsheet

C++ is a powerful, compiled language extending C with object-oriented features. Used for systems programming, game development, high-performance computing. You write it, compile to machine code, and it runs incredibly fast.

Getting Started

Installation

# Install compiler
# macOS
brew install gcc

# Linux
sudo apt-get install g++

# Windows - install MinGW

# Verify
g++ --version

Your First Program

#include <iostream>  // Input/output library

int main() {
    std::cout << "Hello, World!" << std::endl;
    return 0;
}

Compiling and Running

g++ hello.cpp -o hello
./hello

Variables & Types

// Integer types
int age = 25;
short small = 1000;
long big = 1000000;

// Floating point
float price = 19.99f;  // Note: f suffix for float
double value = 3.14159;

// Character
char letter = 'A';

// Boolean
bool isActive = true;

// Auto (deduced type)
auto count = 42;  // int inferred

// Constants
const int MAX_USERS = 100;

// Arrays
int numbers[5] = {1, 2, 3, 4, 5};
std::string names[3] = {"Alice", "Bob", "Charlie"};

Strings

#include <string>

std::string message = "Hello";

// Operations
message.length()                    // 5
message[0]                          // 'H'
message.substr(1, 3)                // "ell"
message + " World"                  // Concatenation
message += "!";                     // Append

// Methods
message.find("ell")                 // Position or npos
message.replace(0, 5, "Hi")         // "Hi World!"

// I/O
std::cout << message << std::endl;  // Print with newline
std::cin >> message;                // Read input

Control Flow

// If statement
int age = 18;
if (age >= 18) {
    std::cout << "Adult" << std::endl;
} else {
    std::cout << "Minor" << std::endl;
}

// Switch
switch (day) {
    case 1:
        std::cout << "Monday";
        break;
    default:
        std::cout << "Other";
}

// Loops
for (int i = 0; i < 5; i++) {
    std::cout << i << std::endl;
}

while (count < 10) {
    count++;
}

do {
    count++;
} while (count < 10);

Functions

// Declaration
int add(int a, int b);

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

// Calling
int sum = add(5, 3);

// Default parameters
void greet(std::string name = "Guest") {
    std::cout << "Hello, " << name << std::endl;
}

greet();           // "Hello, Guest"
greet("Alice");    // "Hello, Alice"

Pointers & References

// Pointer (address of variable)
int x = 10;
int* ptr = &x;     // Pointer to x
std::cout << *ptr; // 10 (dereference)

// Reference (alias)
int& ref = x;      // Reference to x
ref = 20;          // x is now 20

// Pointer operations
int arr[5] = {1, 2, 3, 4, 5};
int* ptr = arr;    // Pointer to first element
std::cout << *(ptr + 1);  // 2 (second element)

Classes & Objects

#include <iostream>

class Person {
public:
    // Member variables
    std::string name;
    int age;

    // Constructor
    Person(std::string n, int a) {
        name = n;
        age = a;
    }

    // Method
    void greet() {
        std::cout << "Hello, I'm " << name << std::endl;
    }
};

// Using the class
int main() {
    Person person("Alice", 25);
    person.greet();  // "Hello, I'm Alice"
    std::cout << person.age << std::endl;  // 25
    return 0;
}

Best Practices

Use modern C++ (C++11 and later)
Prefer references over pointers
Use smart pointers (std::unique_ptr, std::shared_ptr)
STL containers instead of raw arrays
RAII - Resource Acquisition Is Initialization

Summary

C++ combines performance of C with object-oriented features. Used for games, systems software, and high-speed applications.

Key strengths:

Extremely fast - compiles to efficient machine code
Low-level control - direct memory management
Object-oriented - organize complex code
Mature ecosystem - decades of libraries