C - Can someone please show me a very simple example of Interfaces

Question

I'm having trouble understanding how to use interfaces and why they're necessary. Could someone provide me a basic example?

Answer 1

Take this as example

interface IFlyable
{
    void Fly();
}

class Bird : IFlyable
{
    public void Fly() { }
}

class Plane : IFlyable
{
    public void Fly() { }
}

List<IFlyable> things = GetBirdInstancesAndPlaneInstancesMixed();
foreach(IFlyable item in things)
{
   item.Fly();
}

Although Bird and Plane share no common base class other than Object, we can deal with them as a group in our software by utilising the same interface because they have the same "feature": Fly