UVA 10494 - If We Were a Child Again

//做这种题我知道了，以后数字能定多大就定多大，最后就long long int，前面都是把数字定义为int，老是WA
#include <iostream>
#include <string>
#include <sstream>
#include <algorithm>
using namespace std;
int main()
{

	string str1,str2,str3;
	while(cin>>str1>>str2>>str3)
	{
		unsigned long int p = 0;
		unsigned long int n;
		char op = str2[0];
		istringstream(str3)>>n;
		for(int i = 0 ,len = str1.length(); i < len ;++i )
		{
		   unsigned long int temp = p*10+ str1[i]-'0' ;
		   p = temp%n;
		   str1[i] = temp/n;
		}
		if(op == '/')
		{
			transform(str1.begin(),str1.end() , str1.begin() , bind1st(plus<int>(),48));
			int pos = str1.find_first_not_of('0');
			if(pos == string::npos) cout<<"0"<<endl;
			else
				cout<<str1.substr(pos)<<endl;
		}
		else if(op == '%')
		{
			cout<<p<<endl;
		}
	}
	return 0;
}