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");     } } 

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) { }