Login Lock After 3 times failur

void invalid()
{
if(session[i]!=null)
{
i=int.parse(session[i].tostring());

}
i++;
session[i]=i.tostring()
if(i>3)
{
responce.redirect ("aaa.aspx");
session.remove("i");
}
}

Clear All TextBoxes

clear all textboxes in Form

protected void Button1_Click(object sender, EventArgs e)
{

foreach (Control ctrl in Form.Controls)
{
if (ctrl.GetType().ToString() == "System.Web.UI.WebControls.TextBox")
{
((TextBox)ctrl).Text = string.Empty;
}
}
clear all textboxes in Form contain Master Page
//ContentPlaceHolder content1 = (ContentPlaceHolder)Master.FindControl("ContentPlaceHolder1");
foreach (Control ctrl in content1.Controls)
{

if (ctrl.GetType().ToString() == "System.Web.UI.WebControls.Panel")
{
foreach (Control ctr in Panel1.Controls)
{
if (ctr.GetType().ToString() == "System.Web.UI.WebControls.TextBox")
((TextBox)ctr).Text = string.Empty;
}
}
}

foreach (Control c in this.Controls)
{
if (c.GetType().ToString () == "TextBox")
((TextBox)c).Text = string.Empty;
}
}