C++ Quick Syntax Cheat Sheet

#include <iostream>
using namespace std;

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

if (score >= 90) {
    cout << "A";
} else if (score >= 60) {
    cout << "Pass";
} else {
    cout << "Fail";
}

switch (op) {
    case '+': cout << a + b; break;
    case '-': cout << a - b; break;
    default:  cout << "Error";
}

// For loop
for (int i = 0; i < 5; i++) {
    cout << i << " ";
}

// While loop
int i = 0;
while (i < 5) {
    cout << i << " ";
    i++;
}

// Do-while loop
int i = 0;
do {
    cout << i << " ";
    i++;
} while (i < 5);

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

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

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

// 1D Array
int marks[5] = {90, 85, 77, 92, 80};
int first = marks[0];

// 2D Array
int matrix[2][3] = {
    {1, 2, 3},
    {4, 5, 6}
};
int val = matrix[0][1]; // 2

// Char Array (C-string)
char msg[6] = "Hello"; // includes \0

// std::string (C++)
#include <string>
string name = "Ali";
name += " Ahmed"; // concatenation

struct Point {
    int x;
    int y;
};

Point p1 = {10, 20};
p1.x = 15; // dot access

Point* ptr = &p1;
ptr->y = 25; // pointer access

int num = 10;
int* ptr = # // Pointer (stores address of num)
int& ref = num;  // Reference (alias for num)

*ptr = 20;       // Changes num to 20
ref = 30;        // Changes num to 30

// Recursive function
int factorial(int n) {
    if (n <= 1) {
        return 1; // Base case
    }
    return n * factorial(n - 1); // Recursive call
}

#include <fstream>
using namespace std;

// Writing to file
ofstream out("data.txt");
out << "Line 1" << endl;
out.close();

// Reading from file
ifstream in("data.txt");
string line;
if (in.is_open()) {
    while (getline(in, line)) {
        cout << line << endl;
    }
    in.close();
}

#include <vector>
using namespace std;

vector<int> vec = {10, 20, 30};
vec.push_back(40); // Adds 40 to the end
int len = vec.size(); // len is 4

// Traversal
for (int x : vec) {
    cout << x << " ";
}

#include <cmath>     // pow(x,y), sqrt(x), abs(x)
#include <iomanip>   // setw(w), setprecision(p)
#include <algorithm> // sort(), max(), min(), swap()

cout << fixed << setprecision(2) << 3.14159; // prints 3.14
sort(arr, arr + 5); // Sorts array ascending