C++

C++ Cheatsheet

Basic Structure

#include <iostream>
using namespace std;

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

Data Types

int x = 5;              // Integer
float f = 3.14f;        // Floating point
double d = 3.14159;     // Double precision
char c = 'A';           // Character
bool b = true;          // Boolean
string s = "Hello";     // String (requires #include <string>)
auto a = 10;            // Auto type deduction

Input/Output

cout << "Output" << endl;           // Output
cin >> variable;                    // Input
printf("Format %d", value);         // C-style output
scanf("%d", &variable);             // C-style input

Operators

// Arithmetic: +, -, *, /, %, ++, --
// Comparison: ==, !=, <, >, <=, >=
// Logical: &&, ||, !
// Bitwise: &, |, ^, ~, <<, >>
// Assignment: =, +=, -=, *=, /=, %=

Control Structures

// If-Else
if (condition) {
    // code
} else if (condition2) {
    // code
} else {
    // code
}

// Switch
switch(variable) {
    case 1:
        // code
        break;
    case 2:
        // code
        break;
    default:
        // code
}

// Ternary
result = (condition) ? value1 : value2;

Loops

// For loop
for (int i = 0; i < 10; i++) {
    // code
}

// While loop
while (condition) {
    // code
}

// Do-While loop
do {
    // code
} while (condition);

// Range-based for loop (C++11)
for (auto element : container) {
    // code
}

Functions

// Function declaration
int add(int a, int b);

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

// Function with default parameters
void display(int x = 10);

// Function overloading
int add(int a, int b);
double add(double a, double b);

// Lambda functions (C++11)
auto lambda = [](int x) { return x * 2; };

Arrays

int arr[5] = {1, 2, 3, 4, 5};
int matrix[3][3];
arr[0] = 10;  // Access element

Pointers

int* ptr;                    // Pointer declaration
ptr = &variable;             // Address-of operator
int value = *ptr;            // Dereference operator
int* arr = new int[10];      // Dynamic allocation
delete[] arr;                // Deallocation

References

int& ref = variable;         // Reference
void swap(int& a, int& b);   // Pass by reference

Classes & Objects

class MyClass {
private:
    int x;
public:
    MyClass();               // Constructor
    ~MyClass();              // Destructor
    void method();           // Method
    static int count;        // Static member
    virtual void func();     // Virtual function
};

MyClass obj;                 // Object creation
MyClass* ptr = new MyClass(); // Dynamic object
delete ptr;

STL Containers

#include <vector>
#include <list>
#include <map>
#include <set>
#include <queue>
#include <stack>

vector<int> v = {1, 2, 3};
v.push_back(4);
v.pop_back();
v.size();

map<string, int> m;
m["key"] = value;

set<int> s = {1, 2, 3};

String Operations

#include <string>

string s = "Hello";
s.length();
s.substr(0, 3);
s.find("ll");
s.append(" World");
s + " World";
s.compare("Hello");

Memory Management

int* p = new int;           // Allocate
delete p;                   // Deallocate

int* arr = new int[10];     // Array allocation
delete[] arr;               // Array deallocation

unique_ptr<int> up(new int); // Smart pointer (C++11)
shared_ptr<int> sp = make_shared<int>(10);

Exception Handling

try {
    // code
    throw exception("Error");
} catch (exception& e) {
    cout << e.what() << endl;
} catch (...) {
    // catch all
}

File I/O

#include <fstream>

ofstream outFile("file.txt");
outFile << "Data" << endl;
outFile.close();

ifstream inFile("file.txt");
string line;
getline(inFile, line);
inFile.close();

Common Algorithms

#include <algorithm>

sort(v.begin(), v.end());
reverse(v.begin(), v.end());
find(v.begin(), v.end(), value);
count(v.begin(), v.end(), value);
max_element(v.begin(), v.end());
min_element(v.begin(), v.end());

Preprocessor Directives

#include <header>
#define PI 3.14159
#ifdef MACRO
#ifndef MACRO
#endif

---

Type Casting

// C-style cast
int x = (int)3.14;

// C++ style casts
static_cast<int>(3.14);           // Compile-time cast
dynamic_cast<Derived*>(basePtr);  // Runtime cast (polymorphic types)
const_cast<int*>(constPtr);       // Remove const
reinterpret_cast<int*>(ptr);      // Low-level reinterpret

Namespace

namespace MyNamespace {
    int value = 10;
    void function() {}
}

using namespace MyNamespace;
using MyNamespace::value;
MyNamespace::function();

namespace alias = MyNamespace;

Enum

// Traditional enum
enum Color { RED, GREEN, BLUE };
Color c = RED;

// Enum class (C++11) - strongly typed
enum class Status { Active, Inactive, Pending };
Status s = Status::Active;

Struct

struct Point {
    int x, y;
    Point(int a, int b) : x(a), y(b) {}
};

Point p = {10, 20};
Point p2(10, 20);

Union

union Data {
    int i;
    float f;
    char c;
};

Data d;
d.i = 10;

Typedef & Using

typedef unsigned long ulong;
typedef int* IntPtr;

using ulong = unsigned long;     // C++11 alias
using IntPtr = int*;

Templates

// Function template
template <typename T>
T max(T a, T b) {
    return (a > b) ? a : b;
}

// Class template
template <class T>
class Container {
    T element;
public:
    void set(T arg) { element = arg; }
    T get() { return element; }
};

// Template specialization
template <>
class Container<char> {
    // specialized implementation
};

// Variadic templates (C++11)
template<typename... Args>
void print(Args... args);

Inheritance

class Base {
protected:
    int value;
public:
    virtual void display() {}
    virtual ~Base() {}
};

// Single inheritance
class Derived : public Base {
public:
    void display() override {}
};

// Multiple inheritance
class Multi : public Base1, public Base2 {};

// Access specifiers: public, protected, private

Polymorphism

// Virtual functions
class Base {
public:
    virtual void show() { cout << "Base"; }
    virtual void pure() = 0;  // Pure virtual (abstract)
};

class Derived : public Base {
public:
    void show() override { cout << "Derived"; }
    void pure() override {}
};

// Function override
void show() override;
void show() final;  // Cannot be overridden further

Operator Overloading

class Complex {
    double real, imag;
public:
    Complex operator+(const Complex& c) {
        return Complex(real + c.real, imag + c.imag);
    }

    Complex operator++();        // Prefix
    Complex operator++(int);     // Postfix

    friend ostream& operator<<(ostream& os, const Complex& c);

    bool operator==(const Complex& c);
    Complex& operator=(const Complex& c);
    double operator[](int index);
};

Friend Functions & Classes

class MyClass {
    int private_data;
    friend void friendFunction(MyClass& obj);
    friend class FriendClass;
};

Static Members

class Counter {
    static int count;
public:
    static int getCount() { return count; }
};

int Counter::count = 0;  // Definition

Const & Constexpr

const int x = 10;
const int* ptr;              // Pointer to const
int* const ptr;              // Const pointer
const int* const ptr;        // Const pointer to const

constexpr int factorial(int n) {  // C++11
    return (n <= 1) ? 1 : n * factorial(n - 1);
}

const int& getRef() const;   // Const member function

Inline Functions

inline int square(int x) {
    return x * x;
}

Function Pointers

int (*funcPtr)(int, int);
funcPtr = &add;
int result = (*funcPtr)(5, 3);
int result = funcPtr(5, 3);  // Also valid

STL Iterators

vector<int>::iterator it;
vector<int>::const_iterator cit;
vector<int>::reverse_iterator rit;

for (it = v.begin(); it != v.end(); ++it) {
    cout << *it;
}

// Iterator operations
advance(it, 3);
distance(it1, it2);
next(it);
prev(it);

STL Algorithms (Extended)

#include <algorithm>
#include <numeric>

// Searching
binary_search(v.begin(), v.end(), value);
lower_bound(v.begin(), v.end(), value);
upper_bound(v.begin(), v.end(), value);

// Modifying
copy(v1.begin(), v1.end(), v2.begin());
fill(v.begin(), v.end(), value);
replace(v.begin(), v.end(), old_val, new_val);
remove(v.begin(), v.end(), value);
unique(v.begin(), v.end());
transform(v.begin(), v.end(), v2.begin(), func);

// Numeric
accumulate(v.begin(), v.end(), 0);
inner_product(v1.begin(), v1.end(), v2.begin(), 0);
partial_sum(v.begin(), v.end(), result.begin());

// Partitioning
partition(v.begin(), v.end(), predicate);

// Set operations
set_union(v1.begin(), v1.end(), v2.begin(), v2.end(), result.begin());
set_intersection(v1.begin(), v1.end(), v2.begin(), v2.end(), result.begin());
set_difference(v1.begin(), v1.end(), v2.begin(), v2.end(), result.begin());

// Min/Max
min(a, b);
max(a, b);
minmax(a, b);  // Returns pair
clamp(value, low, high);  // C++17

Lambda Expressions (C++11)

// Basic lambda
auto lambda = []() { cout << "Hello"; };

// Lambda with parameters
auto add = [](int a, int b) { return a + b; };

// Lambda with capture
int x = 10;
auto capture_by_value = [x]() { return x; };
auto capture_by_ref = [&x]() { x++; };
auto capture_all_by_value = [=]() { return x; };
auto capture_all_by_ref = [&]() { x++; };
auto mixed = [x, &y]() { return x + y; };

// Mutable lambda
auto mut = [x]() mutable { x++; return x; };

// Lambda with return type
auto explicit_return = [](int x) -> double { return x * 1.5; };

Move Semantics (C++11)

// Rvalue references
int&& rref = 10;

// Move constructor
MyClass(MyClass&& other) noexcept;

// Move assignment
MyClass& operator=(MyClass&& other) noexcept;

// std::move
vector<int> v1 = {1, 2, 3};
vector<int> v2 = std::move(v1);  // v1 is now empty

// Perfect forwarding
template<typename T>
void wrapper(T&& arg) {
    func(std::forward<T>(arg));
}

Smart Pointers (C++11)

#include <memory>

// unique_ptr - exclusive ownership
unique_ptr<int> up1(new int(5));
unique_ptr<int> up2 = make_unique<int>(10);  // C++14
unique_ptr<int> up3 = std::move(up2);

// shared_ptr - shared ownership
shared_ptr<int> sp1 = make_shared<int>(5);
shared_ptr<int> sp2 = sp1;  // Reference count = 2
sp1.use_count();
sp1.reset();

// weak_ptr - non-owning reference
weak_ptr<int> wp = sp1;
if (auto sp = wp.lock()) {
    // Use sp
}

Multithreading (C++11)

#include <thread>
#include <mutex>
#include <condition_variable>
#include <atomic>

// Thread
void function() {}
thread t1(function);
thread t2([]() { cout << "Lambda thread"; });
t1.join();
t2.detach();

// Mutex
mutex mtx;
mtx.lock();
// critical section
mtx.unlock();

// Lock guard
{
    lock_guard<mutex> lock(mtx);
    // auto unlock when out of scope
}

// Unique lock
unique_lock<mutex> lock(mtx);
lock.unlock();
lock.lock();

// Atomic
atomic<int> counter(0);
counter++;
counter.fetch_add(1);

Chrono Library (C++11)

#include <chrono>

auto start = chrono::high_resolution_clock::now();
// code
auto end = chrono::high_resolution_clock::now();
auto duration = chrono::duration_cast<chrono::milliseconds>(end - start);

this_thread::sleep_for(chrono::seconds(1));

Random Numbers (C++11)

#include <random>

random_device rd;
mt19937 gen(rd());
uniform_int_distribution<> dis(1, 6);
int random_num = dis(gen);

normal_distribution<> normal(0, 1);
uniform_real_distribution<> real(0.0, 1.0);

Regex (C++11)

#include <regex>

regex pattern("\\\\d+");
string text = "123 abc 456";

// Match
if (regex_match(text, pattern)) {}

// Search
smatch matches;
if (regex_search(text, matches, pattern)) {
    cout << matches[0];
}

// Replace
string result = regex_replace(text, pattern, "X");

Tuple (C++11)

#include <tuple>

tuple<int, string, double> t(1, "hello", 3.14);
auto t2 = make_tuple(1, "hello", 3.14);

int x = get<0>(t);
string s = get<1>(t);

tie(x, s, ignore) = t;  // Unpack

// Structured binding (C++17)
auto [a, b, c] = t;

Optional (C++17)

#include <optional>

optional<int> maybe_value;
optional<int> has_value = 42;

if (has_value) {
    cout << *has_value;
}

int val = has_value.value_or(0);

Variant (C++17)

#include <variant>

variant<int, string, double> v;
v = 42;
v = "hello";

int i = get<int>(v);
if (holds_alternative<string>(v)) {
    string s = get<string>(v);
}

Attributes (C++11+)

[[noreturn]] void terminate();
[[deprecated]] void old_function();
[[nodiscard]] int important();
[[maybe_unused]] int x;
[[fallthrough]]  // In switch statement

Assert & Static Assert

#include <cassert>

assert(x > 0);  // Runtime assertion

static_assert(sizeof(int) == 4, "Ints must be 4 bytes");  // Compile-time