It's a good idea to identify the errors at run time to detect
and handle it. .Net framework has built in mechanism for that.
these exceptions occurs because of user,logic and system errors.

following way a DataTable with data can be used to
populate gridview control in asp.net.following codes get files list
from a file path and adds in DataTable then sets that
DataTable as a DataSource of the GridView grdDirList.

when you submit form with input and select
controls,the values of these controls are
passed with form.we get these as POST var-
$_POST["controlname"];

in php there is a command which is used
to redirect to a page from a page.the following
codes shows hot to achieve this.

Today ajax is being a common part in most large website and
application.user loves the way everything done without page
refresh and website's with ajax implemented is getting higher
popularity.in the following i showed how to use ajax in asp.net
web page.you can use in php too -

It's a very logical requirement to validate user entered email
address before processing anything.in this way you will
never get a invalid email address when you do something
with email address like send email,etc.