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C# C# Objects Inheritance Inheritance

Posted by Ra Bha
Ra Bha
2,201 Points

Keep getting an error despite my code reflecting the Code Challenge instructions. Not sure what to do here

I feel like my code for this challenge reflects the instructions including a Square subclass of class Polygon. However, I keep getting a Bummer: did you define your Square class...error. I am not sure how to fix this.

Polygon.cs 
namespace Treehouse.CodeChallenges
{
    class Polygon
    {
        public readonly int NumSides;
        {

        }
        public Polygon(int numSides)
        {
            NumSides = numSides;
        }
    }
    class Square : Polygon 
    {
        public readonly int SideLength; 
        {
            public Square(int sideLength) : base NumSides(4); 
            {
            }
        }
    }      
}

2 Answers

Mark Sebeck
MOD
Mark Sebeck
Treehouse Moderator 38,304 Points
Mark Sebeck
Mark Sebeck
Treehouse Moderator 38,304 Points

Hi Ra Bha. You're close but I see a few issues. SideLength is a field so remove the brackets after "public readonly int SideLength; "

Also the format for base is just : base(parameter to pass) so here it should be 

public Square(int sideLength) : base (4)

instead of

public Square(int sideLength) : base NumSides(4);

Also don't forget to initialize the SideLength field with the value in the constructor. So you will need something like they have in the Polygon class but with SideLength and sideLength.

Keep at it Ra Bha. Inheritance is not an easy concept. Post your updated code if you are still having issues.

Ra Bha
Ra Bha
2,201 Points
Ra Bha
Ra Bha
2,201 Points

Thank you Mark, this guidance helped me and I resolved the issue.

A couple followup questions just to make sure my understanding of the logic matches the level of Code Challenge completion:

1) I noticed that the statement with the base keyword does not have a semicolon at the end. Would it be correct to think of that as the rule for using base within code? If not, in which circumstances would you not use a semicolon at the end?

2) I understand now that the base keyword passes the parameters from the subclass to the constructor of the class. I realize that the field for the subclass must be initialized, aka

SideLength = sideLength;

But if the base keyword passes the parameter 4 to the constructor of the parent class Polygon, then why isn't code required to initialize NumSides aka 

NumSides = numSides;

?

Thanks, Mark - I really appreciate it.

Mark Sebeck
Mark Sebeck
Treehouse Moderator 38,304 Points
Mark Sebeck
Mark Sebeck
Treehouse Moderator 38,304 Points

You are welcome Ra Bha. Always happy to help. So glad you were able to resolve your issue.

There is no semicolon after base because it is a constructor definition. Just like there is no semicolon after Polygon is declared. Just a bracket 

public Polygon(int numSides)
        {
            NumSides = numSides;
        }

NumSides is being set in the Polygon constructor like you said. That is the advantage of inheritance. Think of it as calling the parent constructor and passing in 4. NumSides will be set to 4 in the Polygon class. I hope that's clear. You kind of almost answered your second question in your question.