stack top() in C++ STL

Stacks are a type of container adaptors with LIFO(Last In First Out) type of work, where a new element is added at one end called the top of the stack and an element is removed from the same end only.

stack::top() top() function is used to reference the top(or the newest) element of the stack.

Syntax :

stackname.top()

Parameters : No value is needed to pass as the parameter.

Return Value: Direct reference to the top element of the stack container.



Examples:

Input  : stackname.push(5);
         stackname.push(1);
         stackname.top();
Output : 1

Input  : stackname.push(5);
         stackname.push(1);
         stackname.push(2);
         stackname.top();
Output : 2

Errors and Exceptions

  1. If the stack container is empty, it causes undefined behaviour
  2. It has a no exception throw guarantee if the stack is not empty
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// CPP program to illustrate
// Implementation of top() function
#include <iostream>
#include <stack>
using namespace std;
  
int main()
{
    stack<int> mystack;
    mystack.push(5);
    mystack.push(1);
    mystack.push(2);
  
    // Stack top
    cout << mystack.top();
    return 0;
}

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Output:


2



Application :

Given a stack of integers, find the sum of the all the integers.


Input : 1, 8, 3, 6, 2
Output: 20



Algorithm


    

  1. Check if the stack is empty, if not add the top element to a variable initialised as 0, and pop the top element.
    2. 

  2. Repeat this step until the stack is empty.
    3. 

  3. Print the final value of the variable.
    4. 












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// CPP program to illustrate 


// Application of top() function 


#include <iostream> 


#include <stack> 


using namespace std; 


  


int main() 


{ 


    int sum = 0; 


    stack<int> mystack; 


    mystack.push(1); 


    mystack.push(8); 


    mystack.push(3); 


    mystack.push(6); 


    mystack.push(2); 


  


    // Stack becomes 1, 8, 3, 6, 2 


  


    while (!mystack.empty()) { 


        sum = sum + mystack.top(); 


        mystack.pop(); 


    } 


    cout << sum; 


    return 0; 


} 



















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Output:


20





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