Can someone review what's wrong with the code

[shh]

Hi
Here is the problem
http://www.spoj.pl/problems/LASTDIG/
Here is the code
but it doesn't accept it what's wrong with it

#include <iostream>
#include <cmath>
using namespace std;
int main()
{
    int c;
    cin >> c;
    for(c; c > 0; c--){
   double a, b, last = 0;
   cin >> a >> b;
    double res = pow(a, b);
    last = res - ((static_cast<int>(res) / 10) * 10);
    cout << last << endl;
}
}

[TripleM_sof]

Doubles can't store the result of a calculation like that accurately enough.