Program.cs

using System;

namespace Attributes
{
    public class Program
    {
        // Multiuse attribute.  
        [System.AttributeUsage(System.AttributeTargets.Class |
                               System.AttributeTargets.Struct |
                               System.AttributeTargets.Method,
                               AllowMultiple = true)  // Multiuse attribute.  
        ]
        public class Author : System.Attribute
        {
            string name;
            public double version;

            public Author(string name)
            {
                this.name = name;

                // Default value.  
                version = 1.0;
            }

            public string GetName()
            {
                return name;
            }
        }

        // Class with the Author attribute.  
        [Author("P. Ackerman")]
        public class FirstClass
        {
            // ...  
        }

        // Class without the Author attribute.  
        public class SecondClass
        {
            // ...  
        }

        // Class with multiple Author attributes.  
        [Author("P. Ackerman"), Author("R. Koch", version = 2.0)]
        public class ThirdClass
        {
            // ...  
        }

        public static void PrintAuthorInfo(System.Type t)
        {
            System.Console.WriteLine("Author information for {0}", t);

            // Using reflection.  
            System.Attribute[] attrs = System.Attribute.GetCustomAttributes(t);  // Reflection.  

            // Displaying output.  
            foreach (System.Attribute attr in attrs)
            {
                if (attr is Author)
                {
                    Author a = (Author)attr;
                    System.Console.WriteLine("   {0}, version {1:f}", a.GetName(), a.version);
                }
            }
        }

        static void Main(string[] args)
        {
            PrintAuthorInfo(typeof(FirstClass));
            PrintAuthorInfo(typeof(SecondClass));
            PrintAuthorInfo(typeof(ThirdClass));
        }

        /* Output:  
            Author information for FirstClass  
               P. Ackerman, version 1.00  
            Author information for SecondClass  
            Author information for ThirdClass  
               R. Koch, version 2.00  
               P. Ackerman, version 1.00  
        */
    }
}