#include <iostream>
using namespace std;

#define MAX_SIZE 100

class Queue {
private:
    int arr[MAX_SIZE];
    int front, rear;

public:
    Queue() {
        front = -1; // Initialize front of the queue
        rear = -1;  // Initialize rear of the queue
    }

    // Function to check if the queue is empty
    bool isEmpty() {
        return front == -1 && rear == -1;
    }

    // Function to check if the queue is full
    bool isFull() {
        return rear == MAX_SIZE - 1;
    }

    // Function to enqueue an element into the queue
    void enqueue(int value) {
        if (isFull()) {
            cout << "Queue Overflow!" << endl;
            return;
        }
        if (isEmpty()) {
            front = rear = 0;
        } else {
            rear++;
        }
        arr[rear] = value;
        cout << "Enqueued " << value << " into the queue." << endl;
    }

    // Function to dequeue an element from the queue
    int dequeue() {
        if (isEmpty()) {
            cout << "Queue Underflow!" << endl;
            return -1; // Return a default value indicating failure
        }
        int value = arr[front];
        if (front == rear) {
            front = rear = -1;
        } else {
            front++;
        }
        cout << "Dequeued " << value << " from the queue." << endl;
        return value;
    }

    // Function to return the front element of the queue without removing it
    int peek() {
        if (isEmpty()) {
            cout << "Queue is empty." << endl;
            return -1; // Return a default value indicating failure
        }
        return arr[front];
    }

    // Function to display all elements of the queue
    void display() {
        if (isEmpty()) {
            cout << "Queue is empty." << endl;
            return;
        }
        cout << "Queue elements: ";
        for (int i = front; i <= rear; ++i) {
            cout << arr[i] << " ";
        }
        cout << endl;
    }
};

int main() {
    Queue queue;
    int choice, value;

    while (true) {
        cout << "\nQueue Operations:" << endl;
        cout << "1. Enqueue" << endl;
        cout << "2. Dequeue" << endl;
        cout << "3. Peek" << endl;
        cout << "4. Display" << endl;
        cout << "5. Exit" << endl;
        cout << "Enter your choice: ";
        cin >> choice;

        switch (choice) {
            case 1:
                cout << "Enter value to enqueue: ";
                cin >> value;
                queue.enqueue(value);
                break;
            case 2:
                queue.dequeue();
                break;
            case 3:
                cout << "Front element: " << queue.peek() << endl;
                break;
            case 4:
                queue.display();
                break;
            case 5:
                cout << "Exiting program." << endl;
                return 0;
            default:
                cout << "Invalid choice! Please try again." << endl;
        }
    }

    return 0;
}
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Read inputs from stdin

OneCompiler's C++ online compiler supports stdin and users can give inputs to programs using the STDIN textbox under the I/O tab. Following is a sample program which takes name as input and print your name with hello.

#include <iostream>
#include <string>
using namespace std;

int main() 
{
    string name;
    cout << "Enter name:";
    getline (cin, name);
    cout << "Hello " << name;
    return 0;
}

About C++

C++ is a widely used middle-level programming language.

  • Supports different platforms like Windows, various Linux flavours, MacOS etc
  • C++ supports OOPS concepts like Inheritance, Polymorphism, Encapsulation and Abstraction.
  • Case-sensitive
  • C++ is a compiler based language
  • C++ supports structured programming language
  • C++ provides alot of inbuilt functions and also supports dynamic memory allocation.
  • Like C, C++ also allows you to play with memory using Pointers.

Syntax help

Loops

1. If-Else:

When ever you want to perform a set of operations based on a condition If-Else is used.

if(conditional-expression) {
   //code
}
else {
   //code
}

You can also use if-else for nested Ifs and If-Else-If ladder when multiple conditions are to be performed on a single variable.

2. Switch:

Switch is an alternative to If-Else-If ladder.

switch(conditional-expression){    
case value1:    
 // code    
 break;  // optional  
case value2:    
 // code    
 break;  // optional  
......    
    
default:     
 code to be executed when all the above cases are not matched;    
}

3. For:

For loop is used to iterate a set of statements based on a condition.

for(Initialization; Condition; Increment/decrement){  
  //code  
}

4. While:

While is also used to iterate a set of statements based on a condition. Usually while is preferred when number of iterations are not known in advance.

while (condition) {  
// code 
}

5. Do-While:

Do-while is also used to iterate a set of statements based on a condition. It is mostly used when you need to execute the statements atleast once.

do {  
 // code 
} while (condition);

Functions

Function is a sub-routine which contains set of statements. Usually functions are written when multiple calls are required to same set of statements which increases re-usuability and modularity. Function gets run only when it is called.

How to declare a Function:

return_type function_name(parameters);

How to call a Function:

function_name (parameters)

How to define a Function:

return_type function_name(parameters) {  
 // code
}