C#

class Animal {}
class Mammal : Animal {}
class Birds : Animal {}
class Fish : Animal {}
class Reptiles : Animal {}
class Amphibian : Animal {}
class Fox : Mammal {}

Fox fox = new Fox();

Mammal mammal = new Fox();

Bird eagle = new Eagle();

Animal animal = fox;
animal = eagle;
animal = mammal;

eagle = fox;

eagle = mammal;

fox = eagle;

public class Animal 
   {
   public void Breathe() {}
   }
public class Bird : Animal 
   {
   public void FlapWings() {}
   }
public class Eagle : Bird 
   {
   public void DiveVeryQuicklyOntoOtherBird(Bird target) {}
   }
...
Bird eagle = new Eagle();
Animal animal = eagle;

eagle.FlapWings();
eagle.Breathe();

eagle.DiveVeryQuicklyOntoOtherBird(myPigeon);

eagle = new Sparrow();

((Eagle)eagle).DiveVeryQuicklyOntoOtherBird(new Sparrow());

private void DoSummat()
   {
   Bird eagle = new Eagle();
   ...
   eagle = new Sparrow();
   ...
   }

int i = 1;
while (true)
   {
   Console.WriteLine(i);
   i = i + 1;
   }

private void DoSummat()
   {
   Bird eagle = new Eagle();
   ...
   Bird eagle = new Sparrow();
   ...
   }

for (int i = 0; i < 10; i++)
   {
   Console.Write($"{i} :");
   for (int i = 100; i < 110; i++)
      {
      Console.Write(i);
      }
   Console.WriteLine();
   }

private void DoSummat(int x)
   {
   int x = 666;
   ...
   }

fox = new animal();

public animal fox { get; set; }
public void DoSummat(animal a)
   {
   fox = a;   
   ...
   }

public void DoSummat(animal a)
   {
   fox = a;   
   ...
   fax = b;
   ...
   }

OriginalGriff wrote:

without the type specifier, what problems might it cause?

Animal fox = new Animal();
var fox = new Animal();

• var x = new SomeType(); is fine.
• var x = SomeMethod(); is bad.

OriginalGriff wrote:

I'm not going to start a flame war

Richard Deeming wrote:

Which is why ...