add isbn fun

Checksums/ISBN/ISBN.csproj

@@ -0,0 +1,8 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net5.0</TargetFramework>
+  </PropertyGroup>
+
+</Project>

Checksums/ISBN/Program.cs

@@ -0,0 +1,83 @@
+using System;
+using System.Linq;
+
+// ISBN-Rechner von Artur, Chris und Fionn
+
+namespace ISBN
+{
+    internal class Program
+    {
+        static void Main(string[] args)
+        {
+            while (true)
+            {
+                string input = GetInput(), mode = "NULL";
+
+                string[] split = input.Select(x => x.ToString()).ToArray();
+
+                if (split.Count() == 10) mode = "VALIDATE";
+                if (split.Count() == 9) mode = "GENERATE";
+
+                if (mode == "NULL")
+                {
+                    Console.WriteLine($"\"{input}\" is no valid input. See the rules above for valid input!");
+                    continue;
+                }
+
+                bool skip = false;
+                int temp = 0;
+
+                for(int i = 0; i < 9; i++)
+                {
+                    string sign = split[i];
+
+                    int parsedInt;
+
+                    if(!int.TryParse(sign, out parsedInt))
+                    {
+                        skip = true;
+                        break;
+                    }
+
+                    temp += parsedInt * (i + 1);
+                }
+
+                if (skip) continue;
+
+                Console.WriteLine(temp);
+
+                temp %= 11;
+
+                string sum = temp == 10 ? "X" : temp.ToString();
+
+                Console.WriteLine($"Calculated Checksum is {sum}.");
+                if (mode == "VALIDATE")
+                {
+                    string inCheck = split[9];
+                    Console.Write($"{inCheck} was given. ");
+                    Console.WriteLine(inCheck == sum ? "They are the same." : "They are not the same.");
+                }
+                Console.WriteLine("\n\n\n");
+            }
+        }
+
+        internal static string GetInput()
+        {
+            while (true)
+            {
+                Console.Write("Pls input complete ISBN (can be only ISBN-10, with ot without checksum, do not include dashes!):\n-> ");
+                string input = Console.ReadLine();
+
+                if (input == null || input == "") continue;
+
+                if (input == "q")
+                {
+                    Console.WriteLine("Bye bye!");
+                    Environment.Exit(0);
+                }
+
+                return input;
+            }
+        }
+    }
+}