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Showing content from https://www.geeksforgeeks.org/cpp/stack-empty-and-stack-size-in-c-stl/ below:

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

Last Updated : 08 Apr, 2025

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.

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

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.

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;
}

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.

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:

It is  used to return whether the stack is empty or not.

It is used to return the number of elements in the stack.

Its syntax is:-
stack_name.empty();

Its syntax is:-
stack_name.size();

Its return type is of boolean.

Its return type is of integer.

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