Question 2: File I/O [8]

Write a function, named countChars, that takes a filename as a string parameter, opens the file, then counts and returns the number of characters in the file. It should return -1 if it was unable to open the file. The function should NOT contain any output statements. 
Sample solution
int countChars(string filename)
{
   ifstream fpin;
   fpin.open(filename.c_str());
   if (fpin.fail()) {
      return -1;
   }
   int count = 0;
   while (!fpin.eof()) {
      char c;
      fpin.get(c);
      if (!fpin.eof()) {
         count++;
      }
   }
   fpin.close();
   return count;
}