Wrong version of .NET Core in one of the projects

Books.ConsoleApp/Books.Console.csproj

@@ -0,0 +1,23 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>netcoreapp2.0</TargetFramework>
+    <RootNamespace>Books.ConsoleApp</RootNamespace>
+    <AssemblyName>Books.ConsoleApp</AssemblyName>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Newtonsoft.Json" Version="11.0.2" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <None Update="books.json">
+      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
+    </None>
+    <None Update="books1.json">
+      <CopyToOutputDirectory>Always</CopyToOutputDirectory>
+    </None>
+  </ItemGroup>
+
+</Project>

Books.ConsoleApp/BooksByAuthor.cs

@@ -0,0 +1,16 @@
+using System.Collections.Generic;
+
+namespace Books.ConsoleApp
+{
+    public class BooksByAuthor
+    {
+        public readonly string Author;
+        public readonly List<Book> Books;
+
+        public BooksByAuthor(string author, List<Book> books)
+        {
+            Author = author;
+            Books = books;
+        }
+    }
+}

Books.ConsoleApp/IEnumerableAndIEnumerator.cs

@@ -0,0 +1,18 @@
+namespace Books.Examples
+{
+
+    public interface IEnumerable<out T>
+    {
+        IEnumerator<T> GetEnumerator();
+    }
+    
+    public interface IEnumerator<out T>
+    {
+        T Current { get; }
+
+        bool MoveNext();
+
+        void Reset();
+    }
+    
+}

Books.ConsoleApp/Output.cs

@@ -65,16 +65,4 @@ namespace Books.ConsoleApp
             }
         }
     }
-
-    public class BooksByAuthor
-    {
-        public readonly string Author;
-        public readonly List<Book> Books;
-
-        public BooksByAuthor(string author, List<Book> books)
-        {
-            Author = author;
-            Books = books;
-        }
-    }
 }

Books.ConsoleApp/Program.cs

@@ -1,71 +1,108 @@
-using System;
+
+#region imports
+using System;
 using System.Collections.Generic;
-using System.Diagnostics.Contracts;
-using System.Globalization;
 using System.Linq;
-using Books.ConsoleApp;
-
+using System.Threading.Tasks;
+#endregion
 namespace Books.ConsoleApp
 {
     class Program
     {
         private static IBooksSource BooksSource = new BooksJsonSource();
-        private static List<BooksByAuthor> BooksByAuthorCatalog = null;
-        static void Main(string[] args)
+
+        // we will use this as global state
+        private static List<BooksByAuthor> BooksByAuthorCatalog;
+
+        public static void Main()
         {
             IEnumerable<Book> books = BooksSource.Read();
+
             BooksByAuthorCatalog = new List<BooksByAuthor>();
             
-
-            while (true)
+            foreach(var book in books)
             {
-                System.Console.WriteLine("\nActions available:");
-                System.Console.WriteLine("1 - Output all books by author (Section 2)");
-                System.Console.WriteLine("2 - Search books by title (Section 3)");
-                System.Console.WriteLine("Any other key - Exit");
-
-                var key = System.Console.ReadKey();
-                switch (key.KeyChar)
+                if (AuthorIsAlreadyCataloged(book.author))
                 {
-                    case '1': Output.BooksByAuthor(BooksSource.Read()); break;
-                    case '2': DoSearch(); break;
-                    default: return;
+                    // there are some(1 or more) books by this author already found and catalogued
+                    var authorCatalogIndex = LocateAuthorAlreadyCataloged(book.author);
+
+                    var existingBooks = BooksByAuthorCatalog[authorCatalogIndex].Books;
+                    existingBooks.Add(book);
+                }
+                else
+                {
+                    CatalogueNewAuthor(book);
                 }
             }
 
+            // now we have an list that has all the authors catalogued
+            OutputBooksByAuthor();
+
+            Console.WriteLine("Finished cataloguing authors. (press a key to exit...)");
+            Console.ReadLine();
         }
 
-        public static void DoSearch()
+        private static bool AuthorIsAlreadyCataloged(string author)
         {
-            var books = BooksSource.Read();
-            while (true)
+            var authorAlreadyCatalogued = false;
+
+            // we'll iterate over the cataloge to find the author - if author's already been cataloged
+            for (int j = 0; j < BooksByAuthorCatalog.Count; j++)
             {
-                System.Console.WriteLine("\nSearch by book title or a part of it. \n^^^^Type 'exit' to go back^^^^");
-                var searchTerm = System.Console.ReadLine();
-                if (searchTerm == "exit")
+                var entry = BooksByAuthorCatalog[j];
+                if (entry.Author == author)
                 {
-                    return;
+                    authorAlreadyCatalogued = true;
+                    break;
                 }
-                if (!string.IsNullOrEmpty(searchTerm))
-                {
-                    var booksByAuthor = Search.ByTitle(books, searchTerm);
-
-                    if (booksByAuthor.Count() == 0)
-                    {
-                        System.Console.WriteLine($"No books found for '{searchTerm}'");
-                    }
-                    else
-                    {
-                        foreach (var b in booksByAuthor)
-                        {
-                            System.Console.WriteLine($"{b.author}: {b.title}");
-                        }
-                    }
-                }
-
-                System.Console.WriteLine("----------------------");
             }
+
+            return authorAlreadyCatalogued;
         }
 
+        private static int LocateAuthorAlreadyCataloged(string author)
+        {
+            var authorCatalogIndex = 0;
+
+            // we'll iterate over the cataloge to find the author's index
+            for (int j = 0; j < BooksByAuthorCatalog.Count; j++)
+            {
+                var entry = BooksByAuthorCatalog[j];
+                if (entry.Author == author)
+                {
+                    authorCatalogIndex = j;
+                    break;
+                }
+            }
+
+            return authorCatalogIndex;
+        }
+
+        private static void CatalogueNewAuthor(Book b)
+        {
+            // there are NONE books by this author already found and cataloged
+
+            var newBooksList = new List<Book> { b };
+            var authorAndBooks = new BooksByAuthor(b.author, newBooksList);
+
+            BooksByAuthorCatalog.Add(authorAndBooks);
+        }
+
+
+        private static void OutputBooksByAuthor()
+        {
+            foreach(var ba in BooksByAuthorCatalog)
+            { 
+                Console.Write("Author: {0,-28} Books: ", ba.Author);
+                foreach (var book in ba.Books)
+                {
+                    Console.Write(book.title + ", ");
+                }
+                Console.Write(Environment.NewLine);
+            }
+        }
     }
+
+ 
 }

Demos/DemoFunc.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using Books.ConsoleApp;
 
 public class DemoFunc
 {
@@ -37,7 +38,8 @@ public class DemoFunc
 
 
         Func<IEnumerable<BooksByAuthor>, string, BooksByAuthor> getGataloguedAuthor =
-            (booksByAuthor, authorName) => {
+            (booksByAuthor, authorName) =>
+            {
                 // can do complex stuff or help in debugging
                 return booksByAuthor.FirstOrDefault(ba => ba.Author == authorName);
             };

Demos/Demos.csproj

@@ -2,7 +2,7 @@
 
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <TargetFramework>netcoreapp2.0</TargetFramework>
+    <TargetFramework>netcoreapp3.0</TargetFramework>
   </PropertyGroup>
 
   <ItemGroup>