Stack in C++ STL

Stacks are a type of container adaptors with LIFO(Last In First Out) type of working, Where insertion and deletion is always performed at the top of the stack.

For creating  a stack, we must include the <stack> header file in our code. We then use this syntax to define the std::stack:

Syntax:
stack<object_type> stack_name;

Functions of stack:

• empty : Test whether container is empty (public member function )
• size : Return size (public member function )
• top : Access next element (public member function )
• push : Insert element (public member function )
• emplace : Construct and insert element (public member function )
• pop : Remove top element (public member function )
• swap : Swap contents (public member function )

#include <iostream>
#include <stack>
using namespace std;
int main() {
	stack<int> s;
	s.push(21);
	s.push(22);
	s.push(24);
	s.push(25);
	
	s.pop();
	s.pop();

	while (!s.empty()) {
		cout << ' ' << s.top();
		s.pop();
	}
}

/*
Output : 
 22 21
*/

Code Explanation:

1. Include the iostream and stack header file or only <bits/stdc++.h> in our code to use its functions.
2. Include the std namespace in our code to use its classes without calling it.
3. Call the main() function. The program logic should be added within this function.
4. Create a stack to store integer values.
5. Use the push() function to insert the value 21, 22, 24, 25 into the stack.
6. Use the pop() function to remove the top element from the stack, that is, 25. The top element now becomes 24.
7. Use the pop() function to remove the top element from the stack, that is, 24. The top element now becomes 22.
8. Use a while loop and empty() function to check whether the stack is NOT empty. The ! is the NOT operator.
9. Printing the current contents of the stack on the console.
10. Call the pop() function on the stack.
11. End of the the while loop and main() function.