diff --git a/83 Stock Market/csharp/Game.csproj b/83 Stock Market/csharp/Game.csproj
index 20827042..849a99d4 100644
--- a/83 Stock Market/csharp/Game.csproj	
+++ b/83 Stock Market/csharp/Game.csproj	
@@ -1,8 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
-
   <PropertyGroup>
     <OutputType>Exe</OutputType>
     <TargetFramework>net5.0</TargetFramework>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
-
 </Project>
diff --git a/83 Stock Market/csharp/src/Company.cs b/83 Stock Market/csharp/src/Company.cs
index 59f40e8d..86c4e4ba 100644
--- a/83 Stock Market/csharp/src/Company.cs	
+++ b/83 Stock Market/csharp/src/Company.cs	
@@ -8,16 +8,22 @@
         /// <summary>
         /// Gets the company's name.
         /// </summary>
-        public string Name { get; init; }
+        public string Name { get; }
 
         /// <summary>
         /// Gets the company's three letter stock symbol.
         /// </summary>
-        public string StockSymbol { get; init; }
+        public string StockSymbol { get; }
 
         /// <summary>
         /// Gets the company's current share price.
         /// </summary>
         public double SharePrice { get; init; }
+
+        /// <summary>
+        /// Initializes a new Company record.
+        /// </summary>
+        public Company(string name, string stockSymbol, double sharePrice) =>
+            (Name, StockSymbol, SharePrice) = (name, stockSymbol, sharePrice);
     }
 }
diff --git a/83 Stock Market/csharp/src/Controller.cs b/83 Stock Market/csharp/src/Controller.cs
index bccfde0c..87a1dc7d 100644
--- a/83 Stock Market/csharp/src/Controller.cs	
+++ b/83 Stock Market/csharp/src/Controller.cs	
@@ -97,10 +97,15 @@ namespace Game
             while (true)
             {
                 View.PromptBuySellCompany(company);
-                if (Int32.TryParse(Console.ReadLine(), out var amount))
-                    return amount;
+
+                var input = Console.ReadLine();
+                if (input is null)
+                    Environment.Exit(0);
                 else
+                if (!Int32.TryParse(input, out var amount))
                     View.PromptValidInteger();
+                else
+                    return amount;
             }
         }
     }
diff --git a/83 Stock Market/csharp/src/Program.cs b/83 Stock Market/csharp/src/Program.cs
index 552d8c9a..8d2b2a98 100644
--- a/83 Stock Market/csharp/src/Program.cs	
+++ b/83 Stock Market/csharp/src/Program.cs	
@@ -11,11 +11,11 @@ namespace Game
         /// </summary>
         private static ImmutableArray<Company> Companies = ImmutableArray.CreateRange(new[]
         {
-            new Company { Name = "INT. BALLISTIC MISSILES",     StockSymbol = "IBM", SharePrice = 100 },
-            new Company { Name = "RED CROSS OF AMERICA",        StockSymbol = "RCA", SharePrice = 85  },
-            new Company { Name = "LICHTENSTEIN, BUMRAP & JOKE", StockSymbol = "LBJ", SharePrice = 150 },
-            new Company { Name = "AMERICAN BANKRUPT CO.",       StockSymbol = "ABC", SharePrice = 140 },
-            new Company { Name = "CENSURED BOOKS STORE",        StockSymbol = "CBS", SharePrice = 110 }
+            new Company("INT. BALLISTIC MISSILES",     "IBM", sharePrice:100),
+            new Company("RED CROSS OF AMERICA",        "RCA", sharePrice:85 ),
+            new Company("LICHTENSTEIN, BUMRAP & JOKE", "LBJ", sharePrice:150),
+            new Company("AMERICAN BANKRUPT CO.",       "ABC", sharePrice:140),
+            new Company("CENSURED BOOKS STORE",        "CBS", sharePrice:110)
         });
 
         static void Main()