how to access child object properties

i am sorry if this has been asked before, but i don't really know if i'm phrasing the question right:

So, let's say i hav开发者_C百科e this classes:

class Shape{
int Area
}

class Triangle:Shape{
string type_of_triangle;
}

class Star:Shape{
int Number_of_Points;
}

and a function that returns a shape typed List wich contains both triangle and shape objects in it. when i try to access triangle's or star's properties, visual studio only let's me access the parent's properties.

So, basically my question is: How can i access the child's properties if the objects are stored in a parent-type variable??

---

Shape unknownShape = new Triangle();

if(unknownShape is Triangle){
    ((Triangle)unknownShape).type_of_triangle;
}

---

I would suggest giving a little more thought to the design of you class hierarchy. Off the top of my head I would propose you can place all of the properties you have defined for your derived shapes within the parent. Further, you might want to consider making some of them methods which return values.

While it is not part of your current example, any shape, including a circle has a finite number of points (a circle simply has zero). A generic "shape_family" property might represent the string classification for the specific derivation of the shape class ("Triangle", "Star", etc).

The shape_subtype might represent specific variations ("Right Triangle", "Isoceles Triangle", etc.). Then, if you define the points as, well, POINTS and add them to a list, you will not only have specified locations for them (if that is not beyond the scope of your program), but you will have a count as well. From there you can probably work out some additional logic to map the sides/verticals, and compute such things as Area, perimeter, etc.

Consider (but please note that I am only now branching into C# and Java from vb.net, so if I butcher the code here, try to focus on the class structure, NOT my syntax . . .):

Edit: 4/22/2011 7:41 AM - Ooops. Forgot to make the Class abstract. If methods on a class are defined as "abstract", then the class itself must be abstract as well, meaning the abstract base cannot be directly instantiated. Here is a link to more info on abstract classes and methods/

public abstract class Shape
{ 
    int Area; 
    string shape_family;
    string shape_subtype;
    list<point> Points

    public int number_of_points()    
    {
        return points.count
    }        
    public abstract int perimeter_lenngth()
    public abstract int area()
}  

class Triangle : Shape { 

    //Example of Triangle-specific implementation:
    public override int perimiter_length {
       //You code to obtain and compute the lengths of the sides
    }

    //Example of Triangle-specific implementation:
    public override int area {
        //Your code to obtain and compute        
    }
}

class Star : Shape{

    //Example of Star-specific implementation:
    public override int perimiter_length {
       //Your code to obtain and compute the lengths of the sides
    }

    //Example of Star-specific implementation:
    public override int area {
        //Your code to obtain and compute        
    }
}

class Circle : Shape {
    point center;
    int radius

    // Example of Circle-specific implementation:
    public override int perimiter_length {
        return 2*3.14*radius
    }

    // Example of Circle-specific implementation:
    public override int area {
        return 3.14*radius^2
    }
}