Here are two available XML parsers written in C:
http://www.jclark.com/xml/expat.html[
^],
http://www.xmlsoft.org/[
^].
Such parsers are unusual. Usually, XML parsers are developed using more advanced languages; C seems impractical.
[EDIT]
OK, finally you told me that you are required to write a parser. Unfortunately, we don't have resource for tutoring, and writing parsers can hardly be explained in the format of the forum.
First, you need to know the XML standard very well:
http://en.wikipedia.org/wiki/XML[
^],
http://www.w3.org/XML/[
^].
This is a very useful resource, as the official XML is formulated poorly:
http://www.xml.com/axml/testaxml.htm[
^].
And you need to learn at least something about parsers. This topic is not so easy. Please see:
http://en.wikipedia.org/wiki/Parsing[
^].
Please see all the references from this Wiki page.
And finally, you will need a lot of patience. Parsing in general is a pretty difficult topic, XML is, by far, not as simple as it seems, and C is very difficult and error prone, not adequate at all for solving such problems. On the bright side, if you do this work well, you can get tremendous experience, both positive and negative. :-)
Good luck,
—SA