Friends Pairing using Recursion in C++

 #include<iostream>

#include<string>

using namespace std;

int friendsPairing(int n) {

    if(n == 1 || n == 2) {

        return n;

    }

    // // single

    // friendsPairing(n-1);

    // // pair

    // (n-1) * friendsPairing(n-2)

    return friendsPairing(n-1) + (n-1) * friendsPairing(n-2);

}

int main() {

    cout << friendsPairing(4) << endl; // 10

return 0;

}

Remove Duplicates using Recursion in C++

 #include<iostream>

#include<vector>

#include<cmath>

using namespace std;

void removeDuplicates(string str, string ans, int i, int map[26]) {

    // Base case

    if(i == str.size()) {

        cout << "ans: " << ans << endl;

    return;

    }

    int mapIdx = (int)(str[i] - 'a');

    if(map[mapIdx]) { // duplicate

            removeDuplicates(str, ans, i+1, map);

    } else {// not duplicate

    map[mapIdx] = true;

    removeDuplicates(str, ans+str[i], i+1, map);

    }

}

int main() {

    string str = "appnnacollege";

    string ans = "";

    int map[26] = {false};

    removeDuplicates(str, ans,0, map);

return 0;

}

Book Library Management (University Question)

 #include <iostream>

#include <string>

#include <vector>

using namespace std;

// Library Book Management System

class Book {

private:

    string title;

    string author;

public:

    Book(string t, string a) {

        title = t;

        author = a;

    }

   

    // Constructor :

    string getTitle() {

        return title;

    }

    string getAuthor() {

        return author;

    }

    void showDetails() {

        cout << "Book: " << title << "\nAuthor: " << author << endl;

    }

};

class Library {

private:

    vector<Book> books;

public:

    // Add a book

    void addBook(string title, string author) {

        books.push_back(Book(title, author));

        cout << "Book added successfully.\n";

    }

    // Remove a book

    void removeBook(string title) {

        for(auto it = books.begin(); it <= books.end(); it++) {

            if(it->getTitle() == title) {

                books.erase(it);

                cout << "Book removed successfully.\n";

                return;

            }

        }

        cout << "Book not found.\n";

    }    

    // Show All Books

    void showAllBooks() {

        if(books.empty()){

            cout << "Library is empty.\n";

            return;

        }

        cout << "\nBooks in Library: \n";

        for(auto& book : books) {

            book.showDetails();

        }

    }

};

int main() {

    Library lib;

    lib.addBook("Book S1", "Deb");

    lib.addBook("Book S2", "Deb");

    lib.addBook("Book S3", "Deb");

    lib.showAllBooks();

    lib.removeBook("Book S2");

    lib.showAllBooks();

    return 0;

}

C. Create a C++ program that uses a function template to find the maximum value between two values of any data type.

#include <iostream>

using namespace std;

template<typename T>

T maxVal(T a, T b) {

    return (a>b) ? a : b;

    /*

    if (a > b) {

        return a;

    } else {

        return b;

    }

    */

    /*

    OR 

    return (a > b) ? a : b is same as if 

    (a > b)

    return a;

    else

    return b;

    */

}

int main() {

    int val1, val2;

    cout << "enter first value : ";

    cin >> val1;

    cout << "\nenter second value : ";

    cin >> val2;

    int findMax = maxVal(val1, val2);

    cout << findMax << " is the max value " << endl;

    return 0;

}

A. Create a C++ program that demonstrates function overloading.

 #include <iostream>

#include <string>

#include <vector>

using namespace std;

// Function overloading - example

class Print {

public:

    void show(int x) {

        cout << "int : "<< x << endl;

    }

    void show(string str) {

        cout << "str: " << str << endl;

    }

    void show(string str2) { // <--- This is the problem ( can't put two functions

under a class when it comes to function overloading....

        cout << "str2: " << str2 << endl;

    }

};

int main() {

    Print ob1;

    ob1.show(45);

    ob1.show("apna college");

    ob1.show("Debadatta Patra");

    return 0;

}

D. Create a C++ class template named Pair that represents a pair of values. (University Topic of OOPs)

#include <iostream>

#include <string>

#include <vector>

using namespace std;

// D. Create a C++ class template named Pair that represents a pair of values. 

template <typename T>

class Pair {

private:

    T A1;

    T A2;

    

public:

    Pair(T val1,T val2) {

        A1 = val1;  // initialize first ehe private variable then the Public variable

        A2 = val2;

    }

    

    // display

    void display() {

        cout << "value A: " << A1 << " \nvalue B: " << A2 << endl;

    }

};

int main() {

    int x, y;

    cout << "enter first value : ";

    cin >> x;

        

    cout << "enter second value : ";

    cin >> y;

    

    Pair<int> class1(x, y);

    

    class1.display();

    

    return 0;

}

Merge Sort in C++ (university dsa topic)

 #include <iostream>

#include <vector>

using namespace std;

void merge(vector<int> &arr, int st, int mid , int end){  // O(n)

    vector<int> temp;

    int i = st, j = mid+1;

    // left to right half traversal

    while(i <= mid && j <= end) {

        if(arr[i] <= arr[j]) {

            temp.push_back(arr[i]);

            i++;a

        } else {

            temp.push_back(arr[j]);

            j++;

        }

    }

    while(i <= mid) {

        temp.push_back(arr[i]);

        i++;

    }

    while(j <= end) {

        temp.push_back(arr[j]);

        j++;

    }

   

    for(int idx=0; idx<temp.size(); idx++) {

        arr[idx+st] = temp[idx];

    }

}

void mergeSort(vector<int> &arr, int st, int end) {

    if(st < end) {

        int mid = st + (end-st)/2;

        mergeSort(arr, st,mid); // left half

        mergeSort(arr, mid+1, mid); // right half

        merge(arr, st, mid ,end);

    }

}

int main() {

    vector<int> arr = {12, 31, 35, 8, 32, 17};

    mergeSort(arr, 0, arr.size()-1); // arr.size()-1 => array ka last index)

    for(int val : arr) {

        cout << val << " ";

    }

    cout << endl;

    return 0;

}

Binary Search in C++ (University Topic)

#include <iostream>

using namespace std;

int binarySearch(int arr[], int size, int element) {

    int low, mid, high;

    low = 0;

    high = size-1;  // high last element thats why

    // Start searching

    while(low<=high) {

        mid = (low+high)/2;

        if(arr[mid]==element) {

            return mid;

    }

        if(arr[mid]<element) {

            low = mid+1;

        }

        else {

            high = mid-1;

        }

    }

    // Searching end

    return -1;

}

int main() {

    // Unsorted array for linear search

    // int arr[] = {1,2,3,4,5,5,6,432,432,4,2342,34};

    // int size = sizeof(arr)/sizeof(int);

    // Sorted array for binary search

    int arr[] = {1,3,5,56,64,73,123,225,444};

    int size = sizeof(arr)/sizeof(int);

    int element = 56;

    int searchIndex = binarySearch(arr, size, element);

    cout << "The element " << element << " was found at index " << searchIndex << endl;

    return 0;

}

Linear Search in C++ (University Topic)

 #include <iostream>

using namespace std;

int linearSearch(int arr[], int size, int element) {

    for(int i=0; i<size; i++) {

        if(arr[i]==element) {

         return i;   

        }

    }

    

    

    return -1;

}

int main() {

    int arr[] = {10, 23,45,56,43,53};

    int size = sizeof(arr)/sizeof(int);

    int element = 56;

    int searchResult = linearSearch(arr, size, element);

    

    cout << "The element " << element << " is at index " << searchResult << endl;

    

    return 0;

}

Tiling problem using Recursion in C++

 #include <iostream>

#include <vector>

using namespace std;

int tilingProblem(int n) { // 2xn

    if(n==0 || n==1) {

        return 1;

    }

    //vertical

    int ans1 = tilingProblem(n-1); // 2x(n-1)

    // horizontal

    int ans2 = tilingProblem(n-2); // 2x(n-2)

    return ans1+ans2;

}

int main() {

    int n = 3;

    cout << tilingProblem(4) << endl;

    return 0;

}

OUTPUT:

5

X to the Power N(Code) using Recursion in C++

 #include <iostream>

#include <vector>

using namespace std;

int pow(int x, int n) { // O(logn)

    if(n==0) {

        return 1;

    }

    int halfPow = pow(x, n/2);

    int halfPowSquare = halfPow * halfPow;

    if(n%2 != 0) {

        //odd

        return x * halfPowSquare;

    }

    return halfPowSquare;

}

int main() {

    cout << pow(2, 10) << endl;

    return 0;

}

OUTPUT:

1024

Last Occurence using Recursion in C++

 #include <iostream>

#include <vector>

using namespace std;

int lastOccur(vector<int> arr, int tar, int i) {

    if(i == arr.size()) {

        return -1;

    }

    int idxFound = lastOccur(arr, tar, i+1);

    if(idxFound == -1 && arr[i] == tar) {

        return i;

    }

    return idxFound;

}

int main() {

    vector<int> arr = {1, 2, 3, 3, 3, 4};

    cout << lastOccur(arr, 45, 0) << endl;  // 4

    return 0;

}

First Occurence using Recursion in C++

 #include <iostream>

#include <vector>

using namespace std;

int firstOccur(vector<int> arr, int i, int target) {

    if(i==arr.size()) {

        return -1;

    }

    if(arr[i] == target)

    {

        return i;

    }

    return firstOccur(arr, i+1, target);

}

int main() {

    vector<int> arr = {1, 2, 3, 3, 3, 4};

    cout << firstOccur(arr, 0, 4);

    return 0;

}

Check if Array Sorted using Recursion in C++

#include <iostream>

using namespace std;

bool isSorted(int arr[],int n, int i) {

    if(i == n-1) {

        return true;

    }

    if(arr[i] > arr[i+1]) {

        return false;

    }

    return isSorted(arr, n, i+1);

}

int main() {

    int arr1[5] = {1,2,3,4,5}; // sorted : 1

    int arr2[5] = {1,2,4,3,5}; // unsorted : 0

    cout << isSorted(arr2, 5, 0) << endl;

    return 0;

}

OUTPUT:

0

Nth Fibonacci (Code) Using Recursion in C++

 #include <iostream>

using namespace std;

int fibonacci(int n) {

    if(n == 0 || n == 1) {

        return n; // 0, 1

    }

    return fibonacci(n-1)+fibonacci(n-2);

}

int main() {

    cout << fibonacci(3) << endl;

    return 0;

}

OUTPUT:

2

Sum of N natural numbers using Recursion in C++

 #include <iostream>

using namespace std;

// sum of N natural numbers

int sum(int n) {

    if(n==1) {

        return 1;

    }

    return n+sum(n-1);

}

int main() {

   

    cout << sum(5) << endl;

    return 0;

}

Stack Overflow in C++

 #include <iostream>

using namespace std;

// stack overflow

void func() {

    cout << "function called..kaam\n";

    func();

}

int main() {

    func();

    return 0;

}

Number in Decreasing order in Recursion in C++

 #include <iostream>

using namespace std;

// to print in decreasing order , n = 5

void print(int n) {

    if(n==0) {

        return;

    }

    cout << n << " "; // kaam

    print(n-1); // faith, next call

}

int main() {

    print(5);

    return 0;

}

OUTPUT:

5 4 3 2 1

Factorial in Recursion Memory in C++

 #include <iostream>

using namespace std;

// factorial

int factorial(int n) {

    if(n==0) { // base case - where solution is known (smallest problem)

        return 1;

    }

    return n * factorial(n-1);  // 6 * 5 * 4!

}

int main() {

    int ans = factorial(4); // initialize the answer

    cout << ans << endl; // display result

    return 0;

}

What is recursion? in C++

 Recursion:

A function that repeatedly calls itself.

CODE:

#include<iostream>

using namespace std;

// recursive function -> recursion..

void func() {
cout << "function call...work\n";

func(); // calls itself 

}

int main() {
func();

return 0;

}

OUTPUT:-

function call..work

function call..work

function call..work

function call..work

function call..work

...

.

..

infinite times, until a base case is declared(Smallest problem, where solution is known)..

Object-Oriented Programming: Creating a Student Class from Person Base Class (Assignment Question 3)

 #include <iostream>

using namespace std;

class Person {

public:

    string name; // mistakes -> char name();

    int age; // mistakes -> int age();

};

class Student : public Person {

public:

     void displayStudentInfo(string id) {

        cout << "(" << name << "\", " << age << " ,\"" << id << "\")";  // in order to put double quotations please put \ then " so-> \" this is how it will work

        }

       

};

int main() {

    Student student;

    student.name = "\"Deb";

    student.age = 17;

    student.displayStudentInfo("S12345");

    return 0;

}

OUTPUT:

("Deb", 17 ,"S12345")

Bank Account Assigment Question in OOPs

 #include <iostream>

using namespace std;

class BankAccount {

private:

    int accNumber;

    float balance;

public:

    // Constructor

    BankAccount(int accNum, double bal) {

        accNumber = accNum;

        balance = bal;

    }

    // Deposit money

    void deposit(double amount) {

        balance += amount;

        cout << "Deposited: " << amount << endl;

    }

    // Withdraw money

    void withdraw(double amount) {

        if (amount <= balance) {

            balance -= amount;

            cout << "Withdrawn: " << amount << endl;

        } else {

            cout << "You have insufficient balance." << endl;

        }

    }

    // Get current balance

    void getBal() {

        cout << "Your account balance: " << balance << endl;

    }

};

int main() {

    BankAccount raju(123456789, 1000.00);  // Account with ₹1000

    raju.deposit(200);     // Deposit ₹200

    raju.withdraw(500);    // Withdraw ₹500

    raju.getBal();         // Check balance

    return 0;

}

OUTPUT:

Deposited: 200 Withdrawn: 500 Your account balance: 700

Complex Number Class with Subtraction Operator Overloading in OOPs (Assignment Question 1)

 #include <iostream>

using namespace std;

// Complex Number Substraction Code using Operator Overloading

class Complex {

private: 

    int real, img;

public:    

    Complex(int r, int i) {

        real = r;

        img = i;

        

    }

    

    void showNum() {

        cout << real << " - " << img << "i\n";

    }

    

    

    // Operator Overloading 

    void operator-(Complex &c2) {  // &c2 is value of reference..

    

        int resReal = this->real - c2.real; // result of real

        int resImg = this->img - c2.img; // result of image

        Complex c3(resReal, resImg); // taking both objects of resReal , resImg.

        c3.showNum(); // display the result

    }

    

};

int main()

{   

    Complex c1(2, 4);

    Complex c2(1, 2);

    

    c1.showNum();

    c2.showNum();

    

    c1-c2;

    

    return 0;

}

Predicting the output of friend function and class in OOPs - 02

 #include <iostream>

using namespace std;

class Base

{

public:

    virtual void print() {

        cout << "Base\n";

    }

};

class Derived : public Base {

public:

    void print() {

        cout << "Derived\n";

    }

};

int main() {

    Base *b = new Derived();

    b->print();

    delete b;

    return 0;

}

Predicting the output of Friend class and function problem 1 in OOPs

 #include <iostream>

using namespace std;

class Parent {

public:

    Parent() {

        cout << "constructor of parent\n";

    }

    // destructor of Parent class

    ~Parent() {

        cout << "destructor of parent\n";

    }

};

class Child : public Parent {

public:

    Child() {

        cout << "constructor of child\n";

       

    }

     

    //Destructor of Child

    ~Child() {

        cout << "destructor of child\n";

    }

};

int main() {

    Child ch1;

    return 0;

}

OUTPUT:

constructor of parent

constructor of child

destructor of child

destructor of parent

Friend functions & class in OOPs

 #include <iostream>

using namespace std;

class A {

    string secret = "secret data";

    friend class B;

    friend void revealSecret(A &obj);

};

class B {  // becomes a friend class of A

public:

    void showSecret(A &obj) {

        cout << obj.secret << endl;

    }

};

void revealSecret(A &obj) {

    cout << obj.secret << endl;

}

int main() {

    A a1;

    B b1;

    // b1.showSecret(a1);

    revealSecret(a1);

    return 0;

}

Static keyword : Static Object in OOPs

#include <iostream>

using namespace std;

class Example {

public:

    Example() {

        cout << "constructor..\n";

    }

    ~Example() {

        cout << "destructor..\n";

    }

};

int main() {

    int a = 0;

    if(a == 0) {

        static Example eg1;

    }

    cout << "code ending..\n";

    return 0;

} 

output:

constructor..

code ending..

destructor..

Static Keyword - Static Variable in OOPs (02)

 #include <iostream>

using namespace std;

class Example {

public:

    static int x; // remember to do it const, only way makes it work

};

int Example::x = 0;  // now main func, will share this same object of x.

int main() {

    Example eg1;

    Example eg2;

    Example eg3;

   

    cout << eg1.x++ << endl; // 0

    cout << eg2.x++ << endl; // 1

    cout << eg3.x++ << endl; // 2

    return 0;

}

Static Keyword - Static Variables in OOPs

 #include <iostream>

using namespace std;

void counter() {

    static int count = 0; // Static Variable

    count++;

    cout << "count : " << count << endl;

};

int main() {

    counter();

    counter();

    counter();

    return 0;

}

output:

count : 1

count : 2

count : 3

Pure Virtual Function in OOPs

 #include <iostream>

using namespace std;

// abstract class

class Shape {

public:

    virtual void draw() = 0; //abstract fnx, pure-virtual fnx

};

class Circle : public Shape {

public:

    void draw() {

        cout << "draw circle\n";

    }

};

class Square : public Shape {

public:

    void draw() {

        cout << "draw square\n";

    }

};

int main() {

    Circle c1;

    c1.draw();

    Square sq1;

    sq1.draw();

    return 0;

}

output:

draw circle

draw square