intro_to_queue.cpp

#include<bits/stdc++.h>
using namespace std;

#define n 100

class Queue {
    int* arr;
    int front;
    int back;

    public:
        Queue() {
            arr = new int[n];
            front = -1;
            back = -1;
        }

        void push(int x) {
            if(back == n-1) {
                cout<<"Queue overflow"<<endl;
                return;
            }

            back++;
            arr[back] = x;

            if(front == -1) {
                front++;
            }
        }

        void pop() {
            if(front==-1 || front>back) {
                cout<<"No elements in queue"<<endl;
                return;
            }

            front++;
        }

        int peek() {
            if(front==-1 || front>back) {
                cout<<"No elements in queue"<<endl;
                return -1;
            }

            return arr[front];
        }

        bool empty() {
            if(front==-1 || front>back) {
                return true;
            }
            return false;
        }
};

int main() {

    Queue q;
    q.push(1);
    q.push(2);
    q.push(3);
    q.push(4);

    cout<<q.peek()<<endl;
    q.pop();

    cout<<q.peek()<<endl;
    q.pop();

    cout<<q.peek()<<endl;
    q.pop();

    cout<<q.peek()<<endl;
    q.pop();

    cout<<q.empty()<<endl;

    return 0;
}