Which calling method should be used for the function in these function calls:

int main()
{
  int a, b, c;
  int max;
  double avg;

  cin >> a >> b >> c;
  sort(a,b,c);
  max = findmax(a,b,c);
  avg = average(a,b,c);

  cout << a << " " 
       << b << " "
       << c << endl;

  cout << "Max = " << max << endl;
  cout << "Average = " << avg << endl;
  return 0;
}

What should the declarations be for each of these functions?