stack top() in C++ STL

Last Updated : 14 Feb, 2025

In C++, the std::stack::top() is used to find the top element of the std::stack container. It is a member function of std::stack class defined inside the <stack> header file. In this article, we will learn how to find the top element of stack using stack::top() in C++.

Example:

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

int main() {
    stack<int> st;
    st.push(5);
    st.push(11);
  	
  	cout << st.top() << endl;
  
    st.push(9);
  	cout << st.top();
    return 0;
}

Output
11
9

stack::top() Syntax

st.top()

where st is the name of std::stack.

Parameters

  • This function does not take any parameter.

Return Value

  • Return the top element of the stack container.
  • If the stack is empty, its behaviour is undefined.

More Examples of stack::top()

The following examples demonstrates the use of stack::top() function in different scenarios:

Example 1: Finding Top Element of Stack after Pop Operation

C++ 
// C++ Program to illustrate the use of
// stcak::top()
#include <bits/stdc++.h>
using namespace std;

int main() {
    stack<int> st;
    st.push(5);
    st.push(11);
    st.push(9);
	
  	// Top element before pop
    cout << st.top() << endl;
  
  	// Popping the top element
  	st.pop();
  	cout << st.top();
    return 0;
}

Output
9
11

Example 2: Tyring to Find Top Element of Empty Stack

C++ 
// C++ Program to illustrate the use of
// stcak::top()
#include <bits/stdc++.h>
using namespace std;

int main() {
  
  	// Empty stack
    stack<int> st;
	
  	// Top element of empty stack
    cout << st.top();
    return 0;
}


Output

Undefined behaviour
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