Thread: Help with my RPN calculator using c++ #include <stack>

Code:

#include <iostream>
#include <stack>


void calculation(int, int, char);
using namespace std;
stack<int> a;

void main(void)
{
	
	bool expression = false;
	char ch;
	char done;
	
	int op1;

	cout << "Reverse Polish Notation : " << endl;
	cout << "Enter expression: " << endl;
	while (!expression)
	{
		cin >> op1;
		cin >> op1;
		cin >> ch;
		
		calculation(op1, op1, ch);
		if (!cin)
			expression = false;
		else
		{
			expression = true;
			//cin >> op1;
			//cin >> op2;
			//cin >> ch;
			//calculation(op1, op2, ch);
		}
	}
	cout << "Your expression is " <<  a.top() << endl;
	system ("pause");
}

void calculation(int oper1, int oper2, char chr)
{
	switch (chr)
	{
		case '+':
			a.push(oper1 + oper2);
			break;
		case '-':
			a.push(oper1 - oper2);
			break;
		case '*':
			a.push(oper1 * oper2);
			break;
		case '/':
			a.push(oper1 / oper2);
			break;
		
	}
}

Guess what, if I let the both variables be op1, then if calculate: why that when i add 3 3 + ; no problem encounter it gives 6.
When i add 2 3 +, it gives 6 instead of 5, i dun understand the logic and error.
When i add 1 2+, it gives 4.