C# text box 11 digit only

Question

private void txtReceiverContact_TextChanged(object sender, EventArgs e)

{

if (System.Text.RegularExpressions.Regex.IsMatch(txtReceiverContact.Text, " ^ [0-9]"))

{

txtReceiverContact.Text = "";

}

}

private void txtReceiverContact_KeyPress(object sender, KeyPressEventArgs e)

{

string senderText = (sender as TextBox).Text;

string senderName = (sender as TextBox).Name;

int cursorPosition = (sender as TextBox).SelectionStart;

if (!char.IsControl(e.KeyChar)

&& !char.IsNumber(e.KeyChar))

{

e.Handled = true;

}

}

== When I will press any letter, message box will appear and show "Input Digit Only!" 

== Digt will not be more than 11 (Eleven)