How to count 1 Object in list of many different Object

Question

I face with problem in c#. I declare list l is Interface and 3 Object extend(dog,cat,bird) I need to count how many dog in list?. how can I do..please help me to solve! thank u.

Answer 1

Edited to illuminate inheritance concern raised by @Slava, where my initial inclination is that a dog is a dog is a dog:

using System;
using System.Collections.Generic;
using System.Linq;

public class Program
{
    public static void Main()
    {
        IList<object> foo = new List<object> {
            new Bird(),
            new Cat(),
            new Cat(),
            new Dog(),
            new Bird(),
            new Poodle(),
            new Cat(),
            new Dog(),
            new Husky(),
            new Dachshund(),
            new Poodle(),
            new Cat(),
            new Dog()
        };
        var dogCount = foo.Count(x => x is Dog);
        Console.WriteLine($"{dogCount} dogs.");
    }
}

public class Dog
{
    public virtual string Sound { get { return "Woof"; } }
}

public class Dachshund : Dog
{
    public override string Sound { get { return "Ruff"; } }
}

public class Husky : Dog
{
    public override string Sound { get { return "Yarp"; } }
}

public class Poodle : Dog
{
    public override string Sound { get { return "Yip"; } }
}

public class Cat
{
    public string Sound { get { return "Meow"; } }
}

public class Bird
{
    public string Sound { get { return "Tweet"; } }
}

Working Fiddle here.

Substitute whatever test suits best in the predicate, e.g. instead of x is Dog do x.GetType() == typeof(Dog) if only the specific super-type should be counted.