stackUsingLL.cpp

#include <iostream>
using namespace std;

class Node {
   public:
    int data;
    Node *next;

    Node(int data) {
        this->data = data;
        next = NULL;
    }
};


class Stack {
    Node *head;
    int size;		// number of elements prsent in stack
    
    public :
    
    Stack() {
        head=NULL;
        size=0;
    }
    
    int getSize() {
        return size;
    }
    
    bool isEmpty() {
        return head==NULL;
    }
    
    void push(int element) {
        Node *newNode=new Node (element);
        if(head==NULL)
            head=newNode;
        else{
            newNode->next=head;
            head=newNode; 
        }
       
        size++;
     }
    
    int pop() {
        // Return 0 if stack is empty. Don't display any other message
        if(isEmpty())
            return -1;
        else{
            int ans=head->data;
            Node *temp=head;
            head=head->next;
            delete temp;
            size--;
            return ans;
        }
    }
    
    int top() {
        // Return 0 if stack is empty. Don't display any other message
        if(isEmpty())
            return -1;
        else
            return head->data;
    }
    
  
    
};

int main() {
    Stack st;

    int q;
    cin >> q;

    while (q--) {
        int choice, input;
        cin >> choice;
        switch (choice) {
            case 1:
                cin >> input;
                st.push(input);
                break;
            case 2:
                cout << st.pop() << "\n";
                break;
            case 3:
                cout << st.top() << "\n";
                break;
            case 4:
                cout << st.getSize() << "\n";
                break;
            default:
                cout << ((st.isEmpty()) ? "true\n" : "false\n");
                break;
        }
    }
}