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Stack in C++ STL (Standard Template Library)

C++ STL Stack: Here, we are going to learn about the stack in C++ STL, how to implement a stack using C++ standard template library?
Submitted by Radib Kar, on February 03, 2019

Stack in data structure

The stack is an ordered list where insertion and deletion are done from the same end, top. The last element that entered first is the first one to be deleted (the basic principle behind the LIFO). That means it is a data structure which is implemented as LIFO.

The main stack operations are (basic ADT operations):

1. push (T data): Insertion at top
2. T pop(): Deletion from top
3. bool isEmpty(): Checks for stack to be empty

Here, T is the datatype (int/char/float etc)

STL

The Standard Template Library (STL) is a set of C++ template classes to provide common programming data structures and functions such as lists, stacks, arrays, etc. Therefore STACK can be implemented with help of STL too.

STACK in STL

To declare a stack of datatype T:

stack<T> st; //basic STL declarations
e.g.: 
stack<int> st; //stack to hold integers only

To declare the stack iterator:

stack<T>::iterator it;
e.g.:
stack<int>::iterator it;

C++ STACK Functions

• push(T item) - Inserts an item on top
• pop() - Pops the top element, it doesn't return the popped item
• top() - Returns the top element
• empty - Returns true or false based on whether stack is empty
• size() - Returns size of the stack

You can click on each function to check detailed code and implementation of each function. Below is the assemble of a total stack operation.

C++ STL Stack Implementation

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

int main() {
  cout << "...STACK STL...\n";
  stack<int> st;  // declare the stack

  cout << "enter 0 to stop pushing else enter any other integer\n";
  int num, count = 0;
  cin >> num;
  while (num != 0) {
    st.push(num);  // push function
    cin >> num;
  }

  cout << "stack size is: " << st.size() << endl;  // size function

  cout << "popping...\n";
  cout << "stack elements are:\n";
  while (!st.empty()) {                             // stack not empty
    cout << "top element is:" << st.top() << endl;  // print top element
    st.pop();
    count++;
  }

  if (st.empty()) cout << "stack empty\n";

  cout << "stack size is: " << st.size() << endl;  // size function
  cout << count << " pop operation performed total to make stack empty\n";

  return 0;
}

Output

...STACK STL...
enter 0 to stop pushing else enter any other integer
3
7
8
12
-4
0
stack size is: 5
...popping
stack elements are:
top element is:-4
top element is:12
top element is:8
top element is:7
top element is:3
stack empty
stack size is: 0
5 pop operation performed total to make stack empty