Firstly, don't use Convert methods on user input - they throw an exception if teh user makes a mistake. Which makes your app crash ...
For numeric inputs use the appropriate TryParse methods:
int h;
if (!int.TryParse(textBox1.Text, out h))
{
... report problem to user ...
return;
}
Or better, use a NumericUpDown control instead so they can't enter a "bad value".
Secondly, do yourself a favour, and stop using Visual Studio default names for everything - you may remember that "TextBox8" is the mobile number today, but when you have to modify it in three weeks time, will you then? Use descriptive names - "tbMobileNo" for example - and your code becomes easier to read, more self documenting, easier to maintain - and surprisingly quicker to code because Intellisense can get to to "tbMobile" in three keystrokes, where "TextBox8" takes thinking about and 8 keystrokes...
Thirdly, we have no idea what you expected that code to do, or what it does that you didn't expect - remember that we can't see your screen, access your HDD, or read your mind - we only get exactly what you type to work with and we can't run that code in isolation as we have no access to your control or the click event handler.
There are however far too many "magic numbers" in teher for my taste...