c# 4.0 - Does not contain a constructor that takes 0 arguments

Question

I get an error stating "Products does not contain a constructor that takes 0 arguments" from the following code:

public class Products
{
    string id;
    string name;
    double price;
    int soldCount;
    int stockCount;

    public Products(string id, string name, double price, 
                      int soldCount, int stockCount, double tax)
    {
        this.id = id;
        this.name = name;
        this.price = price;
        this.soldCount = soldCount;
        this.stockCount = stockCount;
    }
}

//I have got some get and set values for the code above 
//but it would have been too long to put in here

public class FoodProducts : Products
{
    public FoodProduct()
    {
        Console.WriteLine("This is food product");
    }

    public void Limit()
    {
        Console.WriteLine("This is an Attribute of a Product");
    }
}

question from:https://stackoverflow.com/questions/12138221/does-not-contain-a-constructor-that-takes-0-arguments

Answer 1

Several rules about C# come into play here:

1. Each class must have a constructor (In order to be, well constructed)

2. If you do not provide a constructor, a constructor will be provided for you, free of change, automatically by the compiler.

   This means that the class

   class Demo{}
   

   upon compilation is provided with an empty constructor, becoming

   class Demo{
      public Demo(){}
   }
   

   and I can do

   Demo instance = new Demo();
   

3. If you do provide a constructor (any constructor with any signature), the empty constructor will not be generated

   class Demo{
      public Demo(int parameter){}
   }
   
   Demo instance = new Demo(); //this code now fails
   Demo instance = new Demo(3); //this code now succeeds
   

   This can seem a bit counter-intuitive, because adding code seems to break existing unrelated code, but it's a design decision of the C# team, and we have to live with it.

4. When you call a constructor of a derived class, if you do not specify a base class constructor to be called, the compiler calls the empty base class constructor, so

   class Derived:Base {
      public Derived(){}
   }
   

   becomes

   class Derived:Base {
      public Derived() : base() {}
   }
   

So, in order to construct your derived class, you must have a parameterless constructor on the base class. Seeing how you added a constructor to the Products, and the compiler did not generate the default constructor, you need to explicitly add it in your code, like:

public Products()
{
}

or explicitly call it from the derived constructor

public FoodProduct()
       : base(string.Empty, string.Empty, 0, 0, 0, 0)
{
}