The below code is useful when you don't want to enter any special characters in a cellNo textbox..
1.First select your TextBox and click on Events.
2.Next select and double click on Keypress event and write below code ..
Private void textbox1_KeyPress(object sender,EventArgs e)
{
if(char.IsNumber(e.KeyChar)!=true)
{
e.Handle=true;
}
}
3.if you want to work a BackSpace Key write above code
if(e.keychar=='\u0008')
{
e.Handle=false;
}