From 27601bd3f6ea9e7a42b9ed373da21459126198fe Mon Sep 17 00:00:00 2001
From: "jason.zhu" <jason.zhu@xero.com>
Date: Mon, 15 Feb 2021 04:30:09 +0000
Subject: [PATCH] Finished first C# code

---
 Factorial/Factorial.cs | 60 ++++++++++++++++++++++++++++++++++++++++++
 Factorial/compile.txt  |  3 +++
 2 files changed, 63 insertions(+)
 create mode 100644 Factorial/Factorial.cs
 create mode 100644 Factorial/compile.txt

diff --git a/Factorial/Factorial.cs b/Factorial/Factorial.cs
new file mode 100644
index 0000000..92d5c48
--- /dev/null
+++ b/Factorial/Factorial.cs
@@ -0,0 +1,60 @@
+using System;
+
+public class Functions
+{
+    public static long Factorial(int n)
+    {
+        // Test for invalid input.
+        if ((n < 0) || (n > 20))
+        {
+            return -1;
+        }
+
+        // Calculate the factorial iteratively rather than recursively.
+        long tempResult = 1;
+        for (int i = 1; i <= n; i++)
+        {
+            tempResult *= i;
+        }
+        return tempResult;
+    }
+}
+
+class MainClass
+{
+    static int Main(string[] args)
+    {
+        // Test if input arguments were supplied.
+        if (args.Length == 0)
+        {
+            Console.WriteLine("Please enter a numeric argument.");
+            Console.WriteLine("Usage: Factorial <num>");
+            return 1;
+        }
+
+        // Try to convert the input arguments to numbers. This will throw
+        // an exception if the argument is not a number.
+        // num = int.Parse(args[0]);
+        int num;
+        bool test = int.TryParse(args[0], out num);
+        if (!test)
+        {
+            Console.WriteLine("Please enter a numeric argument.");
+            Console.WriteLine("Usage: Factorial <num>");
+            return 1;
+        }
+
+        // Calculate factorial.
+        long result = Functions.Factorial(num);
+
+        // Print result.
+        if (result == -1)
+            Console.WriteLine("Input must be >= 0 and <= 20.");
+        else
+            Console.WriteLine($"The Factorial of {num} is {result}.");
+
+        return 0;
+    }
+}
+// If 3 is entered on command line, the
+// output reads: The factorial of 3 is 6.
\ No newline at end of file
diff --git a/Factorial/compile.txt b/Factorial/compile.txt
new file mode 100644
index 0000000..5cbbd1e
--- /dev/null
+++ b/Factorial/compile.txt
@@ -0,0 +1,3 @@
+To compile Factorial.cs.
+
+In Windows, open Developer PowerShell for VS 2019, and enter command `csc Factorial.cs`
\ No newline at end of file