stack top() in C++ STL

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:

#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; } 

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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++ 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; } 

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Example 2: Tyring to Find Top Element of Empty Stack

// 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