Add csharp solution for 371 Sum of two integers

Author: SPponmag

csharp/371-Sum-Of-Two-Integers.cs

@@ -0,0 +1,11 @@
+public class Solution {
+    public int GetSum(int a, int b) {
+        while (b != 0)
+        {
+            var carry = a & b;
+            a = a ^ b;
+            b = carry << 1;
+        }
+        return a;
+    }
+}