You seem to be very fond of using floating point variables...
I know this won't actually solve the "real" problem, but surely an employee id is not a double? If they are, who is employe id 3.1415926...?
Are you planning on having options 1.2, 1.3, 1.8 and 2.5 as well? Otherwise either an integer or a char will do fine here (int will be less changes to the code below).
double a, b,d,e,f,g;
cout<<"1. Add an employee"<<endl;
cout<<"2. Modify employee data"<<endl;
cout<<"3. Delete an employee"<<endl;
cout<<"4. Exit this menu"<<endl;