Added PreviousChar() function

Assignment 1/Program.cs

@@ -716,6 +716,30 @@ namespace Assignment_1
             return c;
         }
 
+        /// <summary>
+        /// Reads the previous char
+        /// </summary>
+        /// <param name="s"></param>
+        /// <returns></returns>
+        static char PreviousChar(Stream s)
+        {
+            Stack<byte> charBytes = new Stack<byte>(4);
+            for (int i = 0; i < 4; i++)
+            {
+                if (s.Position == 0)
+                {
+                    break;
+                }
+                s.Position--;
+                byte read = (byte)s.ReadByte();
+                charBytes.Push(read);
+                // No longer an UTF-8 extension, last byte is the final
+                if (read >> 6 != 2) break;
+            }
+            string converted = Encoding.UTF8.GetString(charBytes.ToArray());
+            return converted[0];
+        }
+
         /// <summary>
         /// Skips whitespace characters
         /// </summary>