CODE EXAMPLE FOR HTML

how to write bangladeshi phone number in html

string mobileNumber = "+8801000000000";
if (new Regex(@"^([01]|+88)?d{11}").IsMatch(mobileNumber)){
    MessageBox.Show("Mobile number is valide", "All information is required", MessageBoxButtons.OK, MessageBoxIcon.Asterisk);
}
else{
     MessageBox.Show("Mobile number is not valide", "All information is required", MessageBoxButtons.OK, MessageBoxIcon.Error);
}