class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("Hello World!");
            var cats = new List<Cat>
            {
                new Cat{Name = "Mr Muffins", Weight=10, Age = 4},
                new Cat { Name = "Mr Bigglesworth", Weight = 15, Age = 6 }
            };
            //Sort by name
            cats.Sort(new CatNameComparer());
            //Sort by age
            cats.Sort(new CatAgeComparer());

        }
    }

    class Cat
    {
        public string Name{ get; set; }
        public double Weight { get; set; }
        public int Age { get; set; }
    }

    class CatNameComparer : IComparer<Cat>
    {
        public int Compare([AllowNull] Cat x, [AllowNull] Cat y)
        {
            return new CaseInsensitiveComparer().Compare(x.Name, y.Name);
        }
    }

    class CatAgeComparer : IComparer<Cat>
    {
        public int Compare([AllowNull] Cat x, [AllowNull] Cat y)
        {
            if (x.Age > y.Age)
                return 1;

            if (x.Age < y.Age)
                return -1;

            else
                return 0;
        }
    }