How to implement a Stack using list in C++ STL

In this article, we will discuss how to implement a Stack using list in C++ STL.

Stack is a linear data structure which follows. LIFO(Last In First Out) or FILO(First In Last Out). It mainly supports 4 major operations:
1. Push: Push an element into the stack.
2. Pop: Removes the element by following the LIFO order.
3. Top: Returns the element present at the top of the stack.
4. Empty: Returns whether the stack is empty or not.

Below is the implementation of the above approach:

C++

// C++ implementation of stack
// using list STL
#include <bits/stdc++.h>
using namespace std;

template <typename T>
// templating it so that any data type can be used

class Stack {
public:
    list<T> l;
    int cs = 0;
    // current size of the stack

    // pushing an element into the stack
    void push(T d)
    {
        cs++;
        // increasing the current size of the stack
        l.push_front(d);
    }

    // popping an element from the stack
    void pop()
    {
        if (cs <= 0) {
            // cannot pop us stack does not contain an
            // elements
            cout << "Stack empty" << endl;
        }
        else {
            // decreasing the current size of the stack
            cs--;
            l.pop_front();
        }
    }

    // if current size is 0 then stack is empty
    bool empty() { return cs == 0; }

    // getting the element present at the top of the stack
    T top() { return l.front(); }
    int size()
    {
        // getting the size of the stack
        return cs;
    }

    // printing the elements of the stack
    void print()
    {
        for (auto x: l) {
            cout << x << endl;
        }
    }
};
int main()
{
    Stack<int> s;
    s.push(10); // pushing into the stack
    s.push(20);
    s.push(30);
    s.push(40);
    cout << "Current size of the stack is " << s.size()
         << endl;
    cout << "The top element of the stack is " << s.top()
         << endl;
    s.pop(); // popping from the stack
    cout << "The top element after 1 pop operation is "
         << s.top()
         << endl; // printing the top of the stack
    s.pop(); // popping
    cout << "The top element after 2 pop operations is "
         << s.top() << endl;
    cout << "Size of the stack after 2 pop operations is "
         << s.size() << endl;
    return 0;
}

Output

Current size of the stack is 4
The top element of the stack is 40
The top element after 1 pop operation is 30
The top element after 2 pop operations is 20
Size of the stack after 2 pop operations is 2

Time Complexity: O(1) for both push and pop operations in the stack.
Auxiliary Space: O(N)