C#

private void button1_Click(object sender, System.EventArgs e)<br />
		{<br />
			if(Validate(textBox1.Text))<br />
			{<br />
				Form2 frm =new Form2();<br />
				frm.Show();<br />
			}<br />
			else<br />
			{<br />
				//show your popup window which contain "invalid input" information<br />
			}<br />
			<br />
		}<br />
		private bool Validate(string Val)<br />
		{<br />
			if(Val!="")<br />
			{<br />
				if(Val.Length==9||Val.Length==12)<br />
					return true;<br />
				else<br />
					return false;<br />
			}<br />
			else<br />
				return false;<br />
		}

<br />
///The below given event-handler will only accept integer type.

private void CtextThree_KeyPress(object sender, System.Windows.Forms.KeyPressEventArgs e)<br />
{<br />
	 if(Char.IsDigit(e.KeyChar)) //this will return true if  user typed value is belongs to a char type.<br />
	 e.Handled=false;<br />
	 else<br />
	 e.Handled=true;<br />
			<br />
}<br />