stack empty() and stack size() in C++ STL

The std::stack::size() and std::stack::empty() in C++ are built-in functions that are used to provide information about the size of the stack. They are the member functions of the std::stack container defined inside <stack> header file.

stack::empty()

The stack::empty() method is used to check whether the stack is empty or not.

// C++ program to illustrate how to use
// stack::empty() function
#include <bits/stdc++.h>
using namespace std;

int main() {
    stack<int> st;
  
  	// Checking if the stack st is empty
    if (st.empty())
        cout << "Stack is Empty" << endl;
    else
        cout << "Stack is NOT Empty" << endl;

    // Inserting an element
    st.push(11);

  	// Again checking if the stack st is empty
    if (st.empty())
        cout << "Stack is Empty" << endl;
    else
        cout << "Stack is NOT Empty" << endl;

    return 0;
}

Stack is Empty
Stack is NOT Empty

Syntax

st.empty();

Parameters

• This function does not take any parameter.

Return Value

• Returns true if the stack is empty.
• Returns false if the stack is not empty.

stack::size()

The stack::size() method is used to find the number of elements in the stack container.

// C++ program to illustrate how to use stack::size()
#include <bits/stdc++.h>
using namespace std;

int main() {
    stack<int> st;

    st.push(11);
    st.push(13);
    st.push(9);

    // Finding the size of the stack st
    int n = st.size();
  	cout << "Size : " << n << endl;


    return 0;
}

Size : 3

Syntax

st.size();

Parameters

• This function does not take any parameters.

Return Value

• Returns the number of element present in the stack container.
• If there are no elements in the stack, returns 0.

Difference Between stack::size() and stack::empty()

Both the stack::size() and stack::empty() methods are give the information about the size of stack, but there are some differences between them which are listed below: