class-relationship

I'm learning OOAD and trying to implement class relationship with inheritance but there is an issue here is the code Parent Class namespace ConsoleApplication1 { abstract class Classification { public abstract string type(); } } 1st Child Class namespace ConsoleApplication1 { class FullTime : Classification { bool inCampus; string roomDetail; float rent; public FullTime(string studentRoomDetail, float studentRent) { this.inCampus = true; this.roomDetail = studentRoomDetail; this.rent = studentRent; } public FullTime() { this.inCampus = false; } public string printAccommodationDescription() {