C++ Programming Cheatsheet – STL, OOP Concepts, Syntax

C++ is one of the most widely used programming languages in engineering, competitive programming, and software development. For engineering students, remembering all syntax, concepts, and libraries during exams or interviews can feel overwhelming. That’s where a C++ programming cheatsheet becomes invaluable.

This guide provides a concise yet complete revision of C++ syntax, Object-Oriented Programming (OOP) concepts, and the Standard Template Library (STL). Think of it as your one-stop quick revision notes before coding exams, viva, or placement tests.

Why Use a C++ Cheatsheet?

• Saves revision time before exams or coding contests
• Covers important OOP principles (Inheritance, Polymorphism, Abstraction, Encapsulation)
• Provides ready-to-use STL functions and syntax
• Helps during lab practicals and viva
• Ideal for placements and coding interviews

Basic C++ Syntax Cheatsheet

Structure of a C++ Program

#include <iostream>
using namespace std;

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

Key points:

• #include <iostream> → Input/Output stream header
• using namespace std; → Avoids writing std:: repeatedly
• int main() → Entry point of every program
• cout → Prints output
• cin → Takes input

Data Types in C++

• int → integers
• float → decimal values
• double → higher precision decimals
• char → single character
• string → sequence of characters
• bool → true/false

Variables and Constants

int a = 10;
const float PI = 3.14;

• const keyword makes a variable unchangeable.
• Variables should be initialized before use.

Operators in C++

1. Arithmetic: +, -, *, /, %
2. Relational: ==, !=, <, >, <=, >=
3. Logical: &&, ||, !
4. Bitwise: &, |, ^, ~, <<, >>

Control Structures Cheatsheet

If-Else Statement

if (x > 0) {
    cout << "Positive";
} else {
    cout << "Non-positive";
}

Switch Case

switch (choice) {
    case 1: cout << "One"; break;
    case 2: cout << "Two"; break;
    default: cout << "Invalid";
}

Loops

• For loop

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

• While loop

while(x > 0) {
    cout << x;
    x--;
}

• Do-while loop

do {
    cout << x;
    x--;
} while(x > 0);

Functions in C++

Syntax

return_type functionName(parameters) {
    // code
}

Example:

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

• Function Overloading
  Two or more functions with the same name but different parameters.

int add(int a, int b);
float add(float a, float b);

Object-Oriented Programming (OOP) Concepts Cheatsheet

OOP is the backbone of C++. Let’s quickly revise its four pillars.

1. Encapsulation

Wrapping data and methods into a single unit (class).

class Student {
private:
    int marks;
public:
    void setMarks(int m) { marks = m; }
    int getMarks() { return marks; }
};

2. Inheritance

Reusing properties and methods from another class.

class Animal {
public:
    void eat() { cout << "Eating"; }
};

class Dog : public Animal {
public:
    void bark() { cout << "Barking"; }
};

Types of Inheritance:

• Single
• Multiple
• Multilevel
• Hierarchical
• Hybrid

3. Polymorphism

• Compile-time (Function Overloading, Operator Overloading)
• Runtime (Virtual Functions)

class Shape {
public:
    virtual void draw() { cout << "Drawing shape"; }
};

class Circle : public Shape {
public:
    void draw() override { cout << "Drawing circle"; }
};

4. Abstraction

Hiding implementation details and showing only necessary features.

class Abstract {
    virtual void display() = 0; // Pure virtual function
};

Standard Template Library (STL) Cheatsheet

The STL provides ready-to-use data structures and algorithms. It has four major components:

1. Algorithms
2. Containers
3. Functions
4. Iterators

Common Containers

Vector

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

Stack

#include <stack>
stack<int> s;
s.push(10);
s.push(20);
cout << s.top(); // 20
s.pop();

Queue

#include <queue>
queue<int> q;
q.push(1);
q.push(2);
cout << q.front(); // 1

Priority Queue

#include <queue>
priority_queue<int> pq;
pq.push(30);
pq.push(10);
pq.push(20);
cout << pq.top(); // 30 (max heap)

Map

#include <map>
map<int, string> m;
m[1] = "One";
m[2] = "Two";

Useful STL Functions

• sort(v.begin(), v.end()); → Sort vector
• reverse(v.begin(), v.end()); → Reverse order
• find(v.begin(), v.end(), x); → Search element
• count(v.begin(), v.end(), x); → Count occurrences
• max_element(v.begin(), v.end()); → Find max

Exception Handling in C++

try {
    int x = 0;
    if(x == 0) throw "Division by zero!";
} catch(const char* msg) {
    cout << msg;
}

File Handling Cheatsheet

#include <fstream>
ofstream fout("test.txt");
fout << "Hello File!";
fout.close();

ifstream fin("test.txt");
string line;
while(getline(fin, line)) {
    cout << line;
}
fin.close();

C++ Exam & Placement Tips

• Revise OOP pillars thoroughly
• Practice STL-based coding problems
• Be confident with pointers and memory allocation
• Review common syntax (switch, loops, functions)
• For placements, practice LeetCode, HackerRank, Codeforces problems

Frequently Asked Questions (FAQ)

Q1. What is the best way to revise C++ before exams?
Use a C++ cheatsheet covering syntax, OOP, and STL. Practice 2–3 coding problems daily for confidence.

Q2. What are the four main OOP concepts in C++?
Encapsulation, Inheritance, Polymorphism, and Abstraction.

Q3. Which STL containers are most important for placements?
Vectors, Maps, Sets, Queues, and Priority Queues are frequently used in coding interviews.

Q4. Is STL allowed in coding competitions?
Yes, STL is allowed in most coding contests like Codeforces, CodeChef, and LeetCode.

Q5. How is C++ different from C in terms of OOP?
C is procedural, while C++ supports Object-Oriented Programming with classes and objects.

Conclusion

C++ is not just an academic subject but a powerful language used in real-world software, system design, and competitive coding. With this C++ cheatsheet on syntax, OOP concepts, and STL, you now have a quick reference guide to boost your exam preparation and placement readiness.

Use this as a last-minute revision sheet to quickly brush up concepts, avoid silly mistakes, and perform confidently in labs, exams, and interviews.

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