Adding 2 numbers using stack?

[Gldnbr]

I'm trying to solve this math problem using stacks:

10-4*2+8/10

I know I have to create two different stacks (numbers and operands).

I want to start very simple before I figure out how to do the whole problem.
So, I would like to use this problem:

10+5

I pushed 10 and 5 in the numbers stack and I also pushed + in the operands stack.
But I don't know exactly what to do from there.

I can figure out the top number, which is 5, but how do I get down to the 10?
Also, how do I get it to add each other?

I'm just new to stacks, so if anyone could explain, please do it so I can understand. Thanks.

Here's my attempt which obviously does not work like it's supposed to:

#include <iostream>
#include <stack>
using namespace std;

int main()
{
	stack<int> number;
	stack<char> operand;

	number.push(10);
	number.push(5);
	operand.push('+');

	cout << number.top() << operand.top() << number.top() << endl;

	system("pause");
}

[hamsterman]

Write a function add() that pops the first number from the stack and saves it somewhere, than pops the second one and adds it to the first one. Then pushes the result.

[Gldnbr]

#include <iostream>
#include <stack>
using namespace std;

int add(int a, int b);

int main()
{
	int e, r, z;
	stack<int> number;
	stack<char> operand;

	number.push(10);
	number.push(5);
	operand.push('+');

	if (operand.top() == '+')
	{
	e = number.top();
	number.pop();
	r = number.top();
	cout << e << "+" << r << endl;
	z = add(e, r);
	cout << z << endl;
	}

	system("pause");
}

int add(int a, int b)
{
	int x;
	x = a + b;
	return (x);
}

Thanks!