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C# C# Objects Inheritance Inheritance

Bruno DaSilva
Bruno DaSilva
316 Points
Posted by Bruno DaSilva
Bruno DaSilva
316 Points

C#: Initializing in base constructor

How do I initialize something in the base constructor?

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()
        {
            SideLength = sideLength;
        }
    }

}
Bruno DaSilva
Bruno DaSilva
316 Points
Bruno DaSilva
Bruno DaSilva
316 Points

Also can you explain why when you answer? Thanks :D

3 Answers

Receipt Box
Receipt Box
1,866 Points
Receipt Box
Receipt Box
1,866 Points

Hey Bruno, your code that you initially posted will work, you just need to do two things:

1) Like Seth said, you need to write "base(4)", so that NumSides is set to 4 in the Polygon base constructor.

2) You need a semicolon on line 15, or you'll get a compiler error. (You can click "Preview" to see what the error is)

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(4)
        {
            SideLength = sideLength;
        }
    }

}
Bruno DaSilva
Bruno DaSilva
316 Points
Bruno DaSilva
Bruno DaSilva
316 Points

oh my god... To think I spent like 30 minutes trying to figure out that little tiny mistake before just giving up... Thats sad haha, thanks..

Seth Kroger
Seth Kroger
56,413 Points
Seth Kroger
Seth Kroger
56,413 Points

You do it by passing arguments through base(), and they need to be the same arguments the base class's constructor takes. Because Polygon's constructor takes the number of sides as an argument, you need to pass that through base().

        public Square(int sideLength) : base(4) // A square has 4 sides.
        {
            SideLength = sideLength;
        }
Bruno DaSilva
Bruno DaSilva
316 Points
Bruno DaSilva
Bruno DaSilva
316 Points

Hello I already tried this but for some reason it still doesnt work? If you copy my exact code from above and paste it (with fixing that problem you just pointed out) it still wont work?

Mark Phillips
Mark Phillips
1,749 Points
Mark Phillips
Mark Phillips
1,749 Points

I also spent about 30 minutes trying to figure out what I was doing wrong.

turns out despite it being valid syntax I was setting the parameter and field variables the wrong way round.

Not accepted by the code challenge.

public Square(int sideLength) : base(4)
        {
            sideLength = SideLength;
        }

Accepted by the code challenge.

 public Square(int sideLength) : base(4)
        {
            SideLength = sideLength ;
        }