C#

if (textBox1.Text.Length == 8)
            {
                StringBuilder sb = new StringBuilder();
                sb.Append(textBox1.Text.Substring(0, 2));
                sb.Append("/");
                sb.Append(textBox1.Text.Substring(2, 2));
                sb.Append("/");
                sb.Append(textBox1.Text.Substring(4, 4));
                string displayString = sb.ToString();
                DateTime tmpDateTime;
                if (DateTime.TryParse(displayString, out tmpDateTime))
                {
                    textBox1.Text = displayString;
                }
                else
                {
                    MessageBox.Show("Invalid input.");
                    textBox1.SelectAll();
                }
            }

PIEBALDconsult wrote:

always use an ISO 8601 format: yyyy-MM-dd

(byte)n; // E8
(byte)(n >> 8); // 03

int num = 1000;
byte one = (byte)(0x00FF & num);
byte two = (byte) ((0xFF00 & num) >> 8);

Exception System.OverflowException was thrown in debuggee:
Arithmetic operation resulted in an overflow.

int n = 1000;
System.Diagnostics.Debug.WriteLine((byte)n); // 232
System.Diagnostics.Debug.WriteLine((n >> 8)); // 3

int n = 1000;
byte i = (byte)n;

int n = 1000;
byte i = (byte)n;
System.Diagnostics.Debug.WriteLine(i);