怎么做，求救！

#include <bits/stdc++.h>
using namespace std;
stack<int> s;
char a[10000];
int main()
{
	int t = 0, sum = 0;
	fgets(a, sizeof(a), stdin);
	while (s.empty())
	{
		for (int i = 0; i <= strlen(a); i++)
		{
			s.push(a[i]);
			if (a[i] == '+')
			{
				t = a[i - 1];
				sum += s.top() + t;
				s.pop();
			}
			else if (a[i] == '-')
			{
				t = a[i - 1];			
				sum += abs(s.top() - t);
				s.pop();
			}
			else if (a[i] == '*')
			{
				t = a[i - 1];			
				sum += s.top() * t;			
				s.pop();
			}
			else if (a[i] == '/')
			{
				t = a[i - 1];			
				sum += abs(s.top() / t);			
				s.pop();
			}
			else t = a[i];
		}	
	}
	cout << sum << endl;
}