C++ Programming Cheatsheet

Basic Structure

#include <iostream>
using namespace std;

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

Preprocessor

#include: Includes header files like <iostream>, <string>, <cmath>, <fstream>
#define: Defines constants/macros

Variables

Declaration:
int age;
Initialization:
char grade = 'A';

cout & cin

cout (Output)
cout << "Age: " << age;

cin (Input)
cin >> age;
Note: For strings with spaces, use getline(cin, var);

Data Types & Ranges

Sizes: int(4), float(4), double(8), char(1) bytes
char: -128 to 127
int: -2B to 2B
float: -3.4E+38 to 3.4E+38
double: -1.7E+308 to 1.7E+308

Operators

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

Type Conversion

Implicit: Low → High, safe
int a = 5; float b = a;
Explicit (Casting): High → Low, may lose data
int a = (int)5.5;

Control Structures

Conditional:
if, else if, else
switch-case-break
Unconditional: break, continue
Loops: for, while, do-while

Functions

Declaration:
int add(int, int);
Call:
sum = add(5, 3);
Supports call by value & call by reference.

Types of Functions

1. No args & no return
2. Args & no return
3. No args & with return
4. Args & with return

References

Provides an alias for existing variables

int var = 12;
int& ref = var;  //Reference

1. Declared with & operator
2. Manipulates original value directly
3. Must be initialized when declared
4. Cannot be reassigned

Vectors

Dynamic arrays from STL

#include <vector>
vector<datatype> vector_name;

Commonly used Vector Functions are

push_back(), pop_back(), 
at(i), size(), clear()

Automatically resizes when modified

Pointers

Stores memory address of another variable.

int x = 10;
int *ptr = &x;
*ptr = 20;

*ptr gets the value at x.

Arrays

Collection of same-type elements.
1D: int a[3] = {10, 20, 30};
2D:

int b[2][3] = {
{1, 2, 3},
{4, 5, 6}
};

Strings

Array of characters ending with `\0`.
string name[] = "Imad";
use <string> class for string functions like length(), append(), substr().

String I/O Functions

getline(cin, str) - Reads full line (including spaces)
cin >> str - Reads up to space
s.append("...") - Concatenate
s.find("...") - Search

Structures

Collection of different data types. Each member has its own memory location.

struct Student {
    int id;
    string name;
};
struct Student s1;
s1.id = 101;

Unions

Collection of different data types in the same memory location. Only one member can hold a value at any given time.

union Data {
    int i;
    char str[20];
};

Typedef

Creates an alias for a data type.

typedef struct {
    int id;
    char name[20];
} Student;

Student s1;

Enum

Assigns names to integer constants.

enum Day {SUN, MON};
enum Day d = MON;

Note: Sturcture, Union and Enum are user-defined data types.

Classes & Objects

Classes are blueprint for creating objects.

class MyClass {
  public:
    void display() { 
        cout << "Hello"; 
    }
};
MyClass obj;
obj.display();

OOP Concepts

Encapsulation: Hide data (3 P's)
Inheritance: Acquire properties from another class
Polymorphism: Many forms (overloading/overriding)
Abstraction: Hide implementation details

File Basics

#include <fstream>
int main() {
    // Create and open file
    ofstream MyFile("f.txt");
 
    // Write to the file
    MyFile <<"Hello! world";
 
    // Close the file
    MyFile.close();
}

File Operations

#include <fstream>
ofstream outFile("f.txt");

file << data - Write data
file >> var - Read data
getline(file, str) - Read line
file.close() - Close file
file.is_open() - Check status

File Modes

fstream file;
file.open("f.txt",ios::out);

ios::in - Read mode
ios::out - Write mode
ios::app - Append mode
ios::ate - Start at end
ios::binary - Binary mode

Exception Handling

Handles runtime errors gracefully without stopping program execution.

try{
  //code to try
  throw exception; 
}
catch(){
  //code to handle errors
}

Recursion

A function that calls itself.

return_type func(params) {
  if (base_case)
    return value;
  else
    return func(new_params);
}