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Parsing Html tags using c#

I have html code:
<p>Answer1</p>
<h2>Category1</h2>
<p>Answer2</p>
<p>Answer3</p>
I need to do parsing so that each answer (p) belongs to the category(h2) above.
If nothing is above, then the category will be null.
Look like this :
obj1.category = null; obj1.answer = "Answer1";
obj2.category ="Category1"; obj2.answer = "Answer2";
obj3.category ="Category1"; obj3.answer = "Answer3";
I tried to solve this, but it was useless.

Use HTMLAgilityPack. It will parse HTML and allow you do use LINQ to SELECT whatever you need from the DOM structure.

In addition to HTMLAgilityPack, I've also written a light weight HTML parse for C#.
There's no big secret to the technique, but it's sort of detailed work. You just go through the text character by character and pull out HTML elements.
My parser is on Github as HtmlMonkey.
UPDATE:
I just added support for fairly advanced selectors to easily find nodes within a parsed document.

Using Selenium to select an element with javascript in the href

I have a .NET WebForm and I need to click a link using Selenium and can't use the text content (because of translation issues). How can I identify this element?
registration form
I have tried the following, which does not work:
var element = Driver.FindElementsByXPath($"//*[#href='ctl01']");

The problem is that you are trying to look for an id within the xpath, while the element does not contain an id.
In this case, this should work:
var element = Driver.FindElementsByXPath($"//a[contains(text(), 'registration form')]");
This will only work if all the elements which you are trying to find are links with the text registration form in it.
If you want to find elements on the href, use:
var element = Driver.FindElementsByXPath
("//a[contains(#href, 'javascript:__doPostBack('ctl01','')')]");

Ultimately decided to identify within the href attribute by partial string:
.FindElementsByXPath($"//*[contains(#href, '{id}')]")
This is because putting the whole value of the javascript text into the Selenium call caused it to fail parsing.

try searching for the a href instead of the id like this:
a[#href='javascript:__doPostBack('ctl01','')']
with FindElementsByXPath
then on the var element try using SendKeys like so:
element.SendKeys(Keys.Enter);

Matching tags in C#

I'm trying to match tags with C# and I'm having some trouble getting it to work. I have these tags:
<categories=1></categories=1>
The =1 could be really any number. It could be 1, 2, 3 or any other given number. Is there a way to match this tag in C# using IndexOf or RegEx or a better method.
So to give an example of how I want to use it. I would have something like:
if (PUT WORKING CODE HERE ONCE FIGURED OUT)
{
Do Something
}
Is there an easy way to do this?
Thanks!

I would suggest to first make the document valid XML by replacing those equation signs, then use any XML parser.

there is only one valid answer to this need, unless you are doing homeworks and need to learn how to code this yourself...
avoid reinventing things from scratch and use Html Agility Pack
it is called Html but also handles XML files, in case you have to do more complex things, like parsing, and don't want or cannot use pure XPath and XML related .NET Framework classes.
see here for some examples: How to use HTML Agility pack

Select "src" value with XPath to HtmlAgilityPack

I'm on a development process of a crawling engine. My program crawls websites through Xpath with HtmlAgilityPack. I need to get some image src tag's directly. You can see my simple code below which is not working correctly, thanks in advice!
PS: Please ignore " char problem, XPath patterns are provided by database.
Agility.DocumentNode.SelectSingleNode("//img[#id="product_photo"]/#src");
And this is the line i need to crawl (the *...* part shows block to extract
<img id="product_photo" src="*/images/thumb/4400/10280/st.jpg*">
Some pages provide image in meta tags so .Attributes["src"] wont work.
UPDATE: You can see my query and result here

You cann't get the value of "src" or any other attributes in using:
Agility.DocumentNode.SelectSingleNode(yourXpath);
Just by using:
string s=Agility.DocumentNode.SelectSingleNode(yourXpath).value;
It's because XPath cann't return value of an attribute by SelectSingleNode() func in HtmlAgilityPack class. So you must use SelectSingleNode(yourXpath).value or use Regex after the pharsing to get just the "src" without the outerText.

Regular Expression for Extracting Script Tags

I am trying to write a regular expression in C# to remove all script tags and anything contained within them.
So far I have come up with the following: \<([^:]*?:)?script\>[^(\</<([^:]*?:)?script\>)]*?\</script\>, however this does not work.
I'll break it up and explain my thinking in each section:
\<([^:]*?:)?script\>
Here I am trying to state that it should get any script element, even if it is prefixed with a namespace, say, <a:script></a:script>. I have also added this to the closing tag.
[^(\</<([^:]*?:)?script\>)]*?
Here I am trying to state that it should allow anything to be contained within the tags except for </a:script>, </script>, etc.
\</script\>
Here I am stating that it should have a closing tag.
Can anyone spot where I am going wrong?

This regular expression does the trick just fine:
\<(?:[^:]+:)?script\>.*?\<\/(?:[^:]+:)?script\>
But don't do it please
You will run into a problem by this simple HTML:
<script>
var s = "<script></script>";
</script>
How are you going to solve this problem? It is smarter to use the HTML Agility Pack for such things.

You can't parse HTML with regular expressions.
Use the HTML Agility Pack instead.