Inheritance

As we all know, inheritance is just the hierarchical relationship between various classes.
Class from which another class is inheriting some methods is base class and the other one is known as derived class.

For ex:
Class AA
{ }

Class BB : AA
{ }

Here, AA is your base class and B is your derived class.

Now a very basic question:
When we create an object of derived class, which constructor gets called?
1. Of Base Class
2. Of Derived Class
3. Both
4. None

Let's try to figure it with this example:

class AA
{
public AA()
{
Console.WriteLine("In AA");
}
}

class BB : AA
{
public BB()
{
Console.WriteLine("In BB");
}
}

class CC : BB
{
public CC()
{
Console.WriteLine("In CC");
}
}

Here, class CC is inheriting class BB and class BB is inheriting class AA.

class Program
{
static void Main(string[] args)
{
CC c = new CC();
}
}

I just created an object of CC in another class.
Now which constructor will be called?

Here is the output :


In case of inheritance, derived class always calls base class constructor first and then its own constructor.
Here, object of CC called the constructor of BB and similarly BB calls its base class constructor i.e., AA.
so, the sequence of execution is:
AA constructor -> BB constructor -> CC constructor

Const Keyword

Const is a keyword which can be use to declare fields. We can initialize Const variable only at the time of declaration and cant modify it at runtime.
We cant make a Const field as static.
Const fields are compile-time constants.

For ex:
I have a class which contains two const variables.
class TestConst
{
public const int a = 10;
public const int b = 7;
}

I have another class, where i have created an object of TestConst class.
class Program
{
static void Main(string[] args)
{
Console.WriteLine(TestConst.a);
Console.WriteLine(TestConst.b);
Console.ReadLine();
}
}

We cant access a const variable through object of class. We can always access a const variable with class name only.
Like : ClassName.ConstVariableName

ReadOnly Modifier

ReadOnly is a modifier which can be use to declare fields. We can initialize readonly variable either at the time of declaration or through constructor.

ReadOnly fields can be used for runtime constants as we can declare value through constructors.

For ex:
I have a class which contains two readonly variables.
class TestReadOnly
{
public readonly int a = 10;
public readonly int b;

public TestReadOnly()
{
b = 15;
}

public TestReadOnly(int newB)
{
b = newB;
}
}

I have another class, where i have created an object of TestReadOnly class.
class Program
{
static void Main(string[] args)
{
TestReadOnly test = new TestReadOnly();
Console.WriteLine(test.a);
Console.WriteLine(test.b);
test = new TestReadOnly(20);
Console.WriteLine(test.b);
Console.ReadLine();
}
}

Whenever, I want to reassign the value to a readonly variable, I have to call the parametrized constructor of the class and pass the new value.

PRIME NUMBER

public bool IsPrime(int x)

{

if (x == 1)

{

return true;

}

else

{

for (int i = x - 1; i > 1; i--)

{

if (x % i == 0)

{

return false;

}

}

return true;

}

}

RECURSIVE PROGRAM TO FIND THE FACTORIAL

public int Factorial(int x)

{

if (x == 1)

{

return x;

}

else

{

return x * Factorial(x - 1);

}

}