Random Code Generator using C#

        void generateCode()
        {
          //Initialize variable x as an empty string and a rand varaiable as Random
        String x = "";
        Random rand = new Random();
         // The z string variable holds the current year
        string z = Convert.ToString(DateTime.Now.Year);
 
 
            // This loop creates 2 random numbers at first and concatenates the STI word after the 2 random numbers
            // And also it only generates a number from 0-9
            for (int y = 1; y <= 2; y++)
            {
                x += Convert.ToString(rand.Next(0, 9));
                if (y == 2)
                {
                    x += "STI-";
                }
 
            }
 
           // This loop creates 3 random numbers from 0-9
            for (int y = 1; y <= 3; y++)
            {
                x += Convert.ToString(rand.Next(0, 9));
            }
            //display the generated code in the textbox
            txtIDno.Text =  z + "-" + x;
        }

        private void btnGenerate_Click(object sender, EventArgs e)
        {
            if (txtIDno.Text == "")
            {
                generateCode();
            }
        }