This is the regular expression validation to accept numbers only.

Generally I used to validate textboxes that has to take digits as inputs we can specify range too.

The Regular expression is as follows

@"^\d{0,9}$"

This Regular expression is tested and I would really welcome any corrections and suggestions.

The usage is as follows.

private void button1_Click(object sender, EventArgs e)
{
if (Regex.IsMatch(textBox1.Text, @"^\d{0,9}$"))
{
MessageBox.Show("ok");
}
else
{
MessageBox.Show("is not matched");
}
}

This is code snippet for validating textbox value for numbers between range 0 to 9.