using System.Text.RegularExpressions;
private void btCheckName_Click(object sender, System.EventArgs e)
{
string UserName = this.UserName.Text.Replace("'","''").ToString();
if(UserName!="")
{
Regex regExp = new Regex("^[0-9A-Za-z]{3,16}$");
if(regExp.IsMatch(UserName))
{
.......
}
}
}