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How to use the STL stack in C++

Educative Answers Team

The Standard Template Library (STL) in C++ contains the implementation of commonly known data structures such as arrays, lists, stacks, etc.

To use the STL stack, you must first include the stack file:

#include <stack>

Next, declare an object of type stack and specify the type of elements it will contain using the C++ template syntax.

STL provides the following methods that are​ (usually) associated with a stack:

  1. push(e): Places the element passed as the parameter (e) on top of the stack.

  2. pop(): Returns the top-most element of the stack and removes it.

  3. top(): Returns the top-most element of the stack without removing it.

  4. size(): Returns the total number of elements in the stack.

  5. empty(): Returns true, if the stack is empty, and false if otherwise.

Demo

A stack follows the last-in-first-out (LIFO) principle (i.e., the last element added to the stack is the first to be removed​).

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Code

#include <iostream>
#include <stack>

using namespace std;

int main(){
    stack<int> s;

    // Push elements on the stack:
    s.push(3);
    s.push(5);
    s.push(7);
    
    // Empty the whole stack:
    while(!s.empty()){
        // Print info:
        cout << "top() -> " << s.top() << endl
        << "size() -> " << s.size() << endl << endl;
        
        // Pop out the top element:
        s.pop(); // Can be stored in a variable
    }
}

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stack
c++
data structures
library
stl
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