add great common divisor function

04_quicksort/csharp/06_GetGCD/program.cs

@@ -0,0 +1,31 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+
+namespace GCD
+{
+    public class program
+    {
+
+        //Get great Comman Divisor
+        public static int GetGCD(int FirstNumber, int SecondNumber)
+            => SecondNumber == default ? FirstNumber : GetGCD(SecondNumber, FirstNumber % SecondNumber);
+
+        //Get great Comman Divisor of list
+        public static int GetGCDList(List<int> lst)
+        {
+            var result = lst[0];
+            result = GetGCD(result, lst.Skip(1).FirstOrDefault());
+            return result;
+        }
+
+        static void Main(string[] args)
+        {
+            var lst = new List<int> { 32,696,40,50 };
+            var GCD = GetGCD( 640, 1680);
+            var GCDList = GetGCDList(lst);
+            Console.WriteLine(GCD);
+            Console.WriteLine(GCDList);
+        }
+    }
+}