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stack::empty() function in C++ STL

C++ STL stack::empty() function with example: In this article, we are going to see how to check whether a stack is empty or not using C++ STL?
Submitted by Radib Kar, on February 03, 2019

Prototype:

    stack<T> st; //declaration
    st.empty();

Parameter:

    No parameter passed

Return type: Bool (True or False)

• True: Stack is empty
• False: Stack is not empty

Header file to be included:

    #include <iostream>
    #include <stack>
    OR
    #include <bits/stdc++.h>

Usage:

The function checks whether a stack is empty or not.

Time complexity: O(1)

Example:

    For a stack of integer,
    stack<int> st;
    st.push(4);
    st.push(5);
    stack content:
    5 <-- TOP
    4
    IF (st.empty())
        Print "Stack is empty"
    Else 
        Print "Stack is not empty"
    
    Output:
    Prints "Stack is not empty"
    st.pop()
    st.pop()
    Stack content:
    Empty stack
    IF (st.empty())
        Print "Stack is empty"
    Else 
        Print "Stack is not empty"
    
    Output:
    Prints "Stack is empty"

C++ implementation:

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

int main(){
    cout<<"...use of empty function...\n";
    int count=0;
    stack<int> st; //declare the stack
    st.push(4); //pushed 4
    st.push(5); //pushed 5
    st.push(6);
    
    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()) //to check for empty stack
    cout<<"stack empty\n";
    cout<<count<<" pop operation performed total to make stack empty\n";
	
    return 0;   
}

Output

...use of empty function...
stack elements are:
top element is:6
top element is:5
top element is:4
stack empty
3 pop operation performed total to make stack empty