using System;

public class Program

{

    public void Main()

    {

        var d = new Data();

        d.b = false;

        d.i = 0;

        d.s = null;

        System.Reflection.PropertyInfo[] props = d.GetType().GetProperties();

        foreach(var prop in props) {

            object val = prop.GetValue(d);

            System.Type type = prop.PropertyType;

            Console.WriteLine(val);

            Console.WriteLine(type);

            bool isDefault = true;

            bool isNullable = (type.IsGenericType && type.GetGenericTypeDefinition() == typeof(Nullable<>));

            if(

                (( isNullable|| type.IsValueType == false) && val != null)

                || (!isNullable && type.IsValueType) && val.ToString() != Activator.CreateInstance(type).ToString()

               ) {

                isDefault = false;

            }

            Console.WriteLine(isDefault+System.Environment.NewLine);

        }

    }

}

​

public class Data {

    public bool b {get;set;}

    public int? i {get;set;}

    public int? i2 {get;set;}

    public string s {get;set;}

}