How to resolve C# errors in my code?

Question

I'm a C# beginner (3-day experience). Today I'm practising the inheritance in C#. Here is my code:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Geometry
{
public class Geometry
{
    public double perimeter;
    public double area;
    public bool special;
}

public class Rect : Geometry
{
    public void Rectangle( double length, double width )
    {
        perimeter = (length + width) * 2;
        area = length * width;
        special = (length == width) ? true : false;

        Console.WriteLine("Rectangle information: ");
        Console.WriteLine("Perimeter: " + perimeter);
        Console.WriteLine("Area: " + area);
        if (special) Console.WriteLine("This is a special rectangle. In fact, this is a square!");
        Console.WriteLine();
    }
}

public class Cir : Geometry
{
    public void Circle(double radius)
    {
        perimeter = radius * 2 * Math.PI;
        area = radius * radius * Math.PI;

        Console.WriteLine("Perimeter: " + perimeter);
        Console.WriteLine("Area: " + area);
        Console.WriteLine();
    }
}

public class Main
{
    public static void main(String[] args)
    {
        Rectangle a = new Rectangle(23.00, 21.4);
        Circle b = new Circle(5.8);
    }
}

The compiler said that "The type or namespace of 'Rectangle' could not be found", same as Circle. What's wrong? I don't really understand although I tried many ways to fix them. How can I find and understand the errors?

Answer 1

Read the error. You never wrote a class named Rectangle . Rect is not the same thing.

Answer 2

You have 2 errors.

Error #1 is that your constructor name and your class name are not the same

Error #2 is that the constructor cannot have a return type (void)

public class Rectangle
{
    public Rectangle(double length, double width)
    {
       ...
    }
}

Answer 3

I think you should focus some of your learning on knowing the difference between a class and a method .

In your code you have created the following two classes:

public class Cir : Geometry

public class Rect : Geometry

Yet when you instantiate the classes in your Main() method you do not call them by their class name, instead by the void methods you have defined for each:

Rectangle a = new Rectangle(23.00, 21.4);
Circle b = new Circle(5.8);

What you likely want to do is rename both classes to Rectangle and Circle add a Constructor to each class that takes the parameters you want.

public class Circle : Geometry
{
    public Circle(double radius)
    {
        perimeter = radius * 2 * Math.PI;
        area = radius * radius * Math.PI;
    }
}

Try to keep your methods light, restricting them to a single responsibility or purpose and name the accordingly. For instance in your Geometry class, you could add a void PrintDetails() method or even better a void PrintArea() AND a void PrintPerimeter() method:

public class Geometry
{
    public double perimeter;
    public double area;
    public bool special;

    public void PrintArea()
    {
        Console.WriteLine("Area: " + area);
    }

    public void PrintPerimeter()
    {
        Console.WriteLine("Perimeter: " + perimeter);
    }
}

Answer 4

You can only create instances/objects of classes. Your class names are

Rect 

and

Cir 

Your Object names of these classes here are

a

and

b

respectively. so Your code should be

 Rect  a = new Rect; 
 a.Rectangle(23.00, 21.4); //Calls your method using Rect class object
 Cir  b = new Cir; 
 b.Circle(5.8);//Calls your method using Cir class object

Answer 5

The class you define is "Rect" as example. Now while you may think that is an abbreviation to "Rectangle", the compiler has a more altruistic point of view - it is NOT the same, so error.

Same with "Circ".

Now, both classes have CONSTRUCTORS with the proper name (which thus are not constructors) but the class names themselves - are wrong.

Answer 6

You did not closed the namespace geometry. You can create an instance of Rect(class) or Cir, not Rectangle(method) or Circle.