Infix expression 计算 without '(' and ')'

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

char compare(char tp, char op)
{
	if (((tp == '+' || tp == '-') && (op == '*' || op == '/')) || (tp == '#'))
		return '<';
	return '>';
}

int compute(int n1, int n2, char op)
{
	if (op == '+')
		return n1 + n2;
	else if (op == '-')
		return n1 - n2;
	else if (op == '*')
		return n1*n2;
	else if (op == '/')
		return n2 / n1;
}

int main()
{
	stack<char>num;
	stack<char>oper;

	oper.push('#');

	string s;
	cin >> s;

	for (int i = 0; i<s.length(); i++)
	{
		if (s[i] == '0' || s[i] == '1' || s[i] == '2' || s[i] == '3' || s[i] == '4' || s[i] == '5' || s[i] == '6' || s[i] == '7' || s[i] == '8' || s[i] == '9')
			num.push(s[i]);
		else
		{
			char comp = compare(oper.top(), s[i]);
			if (comp == '<')
				oper.push(s[i]);
			else if (comp == '>')
			{
				int num1 = num.top()-'0';
				num.pop();
				int num2 = num.top()-'0';
				num.pop();
				int result = compute(num1, num2, oper.top());
				num.push(result+'0');
				oper.pop();
				oper.push(s[i]);
			}
		}
	}
	
	if (num.size() != 1)
	{
		while (oper.top() != '#')
		{
			int num1 = num.top()-'0';
			num.pop();
			int num2 = num.top()-'0';
			num.pop();
			int result = compute(num1, num2, oper.top());
			num.push(result+'0');
			oper.pop();
		}
	}

	cout << num.top() << endl;

	return 0;
}