how to generate otp in windows form application in c sharp

protected void GenerateOTP(object sender, EventArgs e)

{

string alphabets = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";

string small_alphabets = "abcdefghijklmnopqrstuvwxyz";

string numbers = "1234567890";

string characters = numbers;

if (rbType.SelectedItem.Value == "1")

{

characters += alphabets + small_alphabets + numbers;

}

int length = int.Parse(ddlLength.SelectedItem.Value);

string otp = string.Empty;

for (int i = 0; i < length; i++)

{

string character = string.Empty;

{

int index = new Random().Next(0, characters.Length);

character = characters.ToCharArray()[index].ToString();

} while (otp.IndexOf(character) != -1);

otp += character;

}

lblOTP.Text = otp;

}