C++ Cheatsheet – A Quick Guide for Beginners & Developers

Content Table

1. Basic Program Structure

#include <iostream>
using namespace std;

int main() {
    cout << "Hello, World!\n";
    return 0;
}

2. Data Types

• int → 4 bytes
• float → 4 bytes (6 decimal places)
• double → 8 bytes (15 decimal places)
• char → 1 byte
• bool → true/false
• string → text
• long, long long → larger ints
• unsigned → no negative numbers

int x = 10;
double pi = 3.14159;
char c = 'A';
bool flag = true;
string s = "Hello";

3. Input & Output

int n;
cin >> n;
cout << "Number: " << n << endl;

4. Operators

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

5. Control Flow

if (x > 0) cout << "Positive";
else if (x < 0) cout << "Negative";
else cout << "Zero";

switch (grade) {
    case 'A': cout << "Excellent"; break;
    default: cout << "Invalid";
}

for (int i=0; i<5; i++) cout << i << " ";
while (n>0) { cout<<n; n--; }
do { cout<<n; } while(n>0);

6. Functions

int add(int a, int b) { return a+b; }
void greet() { cout << "Hello"; }
inline int square(int x) { return x*x; }

7. Arrays & Strings

int arr[5] = {1,2,3,4,5};
for(int i=0;i<5;i++) cout<<arr[i];

string s = "World";
cout << s.size();
s.append("!");

8. Pointers

int x=10;
int *p=&x;
cout << *p; // value
cout << p;  // address

9. References

int a=5;
int &ref=a;
ref=10; // changes a

10. Dynamic Memory

int *ptr = new int(5);
cout << *ptr;
delete ptr;

11. Structures

struct Student {
    string name;
    int age;
};
Student s1={"Ravi",21};

12. Classes & OOP

class Car {
public:
    string brand;
    Car(string b) { brand=b; }
    void drive() { cout<<brand<<" driving\n"; }
};
Car c("BMW");
c.drive();

Access Modifiers

• public → accessible everywhere
• private → accessible inside class only
• protected → accessible in derived classes

13. Constructor & Destructor

class A {
public:
    A() { cout<<"Constructor\n"; }
    ~A() { cout<<"Destructor\n"; }
};

14. Inheritance

class Parent {
public: void speak(){cout<<"Hello";} };
class Child: public Parent {
public: void run(){cout<<"Running";} };
Child c; c.speak(); c.run();

15. Polymorphism

class Base { public: virtual void show(){ cout<<"Base"; } };
class Derived: public Base { public: void show(){ cout<<"Derived"; } };
Base* b = new Derived();
b->show(); // Derived

16. Encapsulation

• Data hidden in private
• Access via getters/setters

17. Abstraction

class Shape {
public: virtual void draw()=0; // pure virtual
};
class Circle: public Shape {
public: void draw(){ cout<<"Circle"; }
};

18. Templates

template<typename T>
T add(T a, T b) { return a+b; }
cout<<add(3,4);
cout<<add(3.5,4.5);

19. Exception Handling

try {
    throw 10;
} catch (int e) {
    cout << "Error: " << e;
}

20. File Handling

ofstream out("data.txt");
out << "Hello File";
out.close();

ifstream in("data.txt");
string line;
while(getline(in,line)) cout<<line;
in.close();

21. STL (Standard Template Library)

Vectors

vector<int> v={1,2,3};
v.push_back(4);
for(int x:v) cout<<x<<" ";

Maps

map<string,int> m;
m["Alice"]=20;
cout<<m["Alice"];

Sets

set<int> s={1,2,3};
s.insert(2);
for(int x:s) cout<<x;

Algorithms

sort(v.begin(), v.end());
reverse(v.begin(), v.end());

22. Smart Pointers (C++11)

#include <memory>
unique_ptr<int> p1(new int(10));
shared_ptr<int> p2 = make_shared<int>(20);

23. Lambda Functions

auto add = [](int a,int b){ return a+b; };
cout<<add(3,4);

24. Namespaces

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

25. Preprocessor

#define PI 3.14
#ifndef PI
#define PI 3.14159
#endif

26. C++11/14/17 Features

• auto type deduction
• Range-based loops
• nullptr
• constexpr
• move semantics
• Structured bindings
• std::optional, std::variant

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