I need help getting started on an XML Parser in C++

I have an assignment that requires creating an XML parser class, in which I can add a string to its instance and then be able to use two functions inside that would turn the string into tokens and add them to an arbitrary type vector;And then check if the string is a valid XML file and both return true if successful.The string has to satisfy XML grammar in order to work.and classify the token as either start tag end tag etc. So I am having trouble getting started with it and how to be able to parse. using conditionals would be very lengthy and inefficient so I was wondering if someone has any insight on this. Thank you