There is a semicolon missing at the end of the header file:
4 5 6 7 8 9 10 11
class Point
{
double x;
double y;
public:
void AskData(void);
double Distance(Point p);
}; // semicolon was missing here
The return type of main() should indeed be int (not void). int main ()
I'm not sure about the sqrt() problem. Sometimes the compiler can't tell whether the argument is type float or double. But in this case everything is of type double already.