How to Declare a Stack in C++?

In C++, Stacks are a type of container adaptor with LIFO(Last In First Out) type of working, where a new element is added at one end (top) and an element is removed from that end only. In this article, we will learn how to declare a stack in C++.

Declaring a Stack in C++ STL

The C++ STL provides a container std::stack that implements stack data structure. To declare a stack, we can use the following syntax

Syntax to Declare a Stack

stack<dataType> stackName;

Here,

• dataType: It is the type of data that a stack will be storing.

C++ Program to Declare A Stack

C++

// C++ Program to illustrate how to declare a stack
#include <iostream>
#include <stack>
using namespace std;

// Driver Code
int main()
{

    // Declaring a stack of integers
    stack<int> stackData;

    // Pushing elements in the stack
    stackData.push(10);
    stackData.push(20);
    stackData.push(30);

    // Printing the top element
    cout << "Top element of the stack is: "
         << stackData.top() << endl;

    // Removing elements from the stack
    stackData.pop();

    // Check if the stack is empty
    if (stackData.empty()) {
        cout << "The stack is empty." << endl;
    }
    else {
        cout << "The stack is not empty." << endl;
    }

    // Printing Size of the stack
    cout << "Size of the stack: " << stackData.size()
         << endl;

    return 0;
}

Output

Top element of the stack is: 30
The stack is not empty.
Size of the stack: 2

Time Complexity: O(N)
Auxiliary Space: O(N), where N is the number of stack elements.