get the sum of stack in c++ without destroying stack

Question

Efficient way of getting sum of stack elements, without emptying it or copying it to other stack? What I am doing is:

    stack<int> si;
    int sum = 0;
    stack<int> tsi(si);
    while (!tsi.empty()) {
        sum += tsi.top();
        tsi.pop();
    }

This can be done using https://ideone.com/i7ha2j midified verson of: https://stackoverflow.com/a/13428630/7267150

Any other way to achieve the requirement (this case, sum)?? I prefer STL (is it possible).

Why do you use `std::stack` to begin with? Just use `std::vector`. — Baum mit Augen, Feb 07 '18 at 14:04
`std::stack` is simply a LIFO data structure. It has not been designed for iterating over elements. — Daniel Langr, Feb 07 '18 at 14:07
The **point** of a stack is that you only get access to one end. If you need something else, such as being able to look at all the values, then a stack is not the right data structure. — Pete Becker, Feb 07 '18 at 14:17
That's not possible for stack.Use vector if you want random access. — ariaman5, Feb 07 '18 at 14:54

score 1 · Accepted Answer · answered Feb 07 '18 at 15:26

You can't iterate over stack so there isn't an easy way. You can use dequeue<int> or stack<int> to insert each top element. Then, use another loop to reinsert them back to original stack<int> si, if you have to use stack. Otherwise, try to switch to vector<int> for easy iteration.

score 0 · Answer 2 · answered Feb 08 '18 at 05:45

Stack isn't the right container to choose here. You should have a look at std::vector, following which you could do something of this sort :

#include <vector>

std::vector< int > vec;
int sum = 0;
for( auto const & it : vec )
{
  sum += it;
}

The main reason for choosing a std::vector over a std::stack is due to the easier capability to iterate over vectors.

get the sum of stack in c++ without destroying stack

2 Answers2