C and C++ (and other languages like FORTRAN, or Pascal, or Visual Basic, or Java or hundreds more) are programming languages with which you specify calculations, actions, and decisions to be carried out in order:
mod curconfig[if left(date,6) = "01-Apr",
t.put "April googlel!",
f.put days('31102005','DDMMYYYY') -
days(sdate,'DDMMYYYY')
" more shopping days to Samhain"];
XML is a markup specification language with which you can design ways of describing information (text or data), usually for storage, transmission, or processing by a program. It says nothing about what you should do with the data (although your choice of element names may hint at what they are for):
<part num="DA42" models="LS AR DF HG KJ"
update="2001-11-22">
<name>Camshaft end bearing retention circlip</name>
<image drawing="RR98-dh37" type="SVG" x="476"
y="226"/> <maker id="RQ778">Ringtown Fasteners Ltd</maker>
<notes>Angle-nosed insertion tool <tool
id="GH25"/> is required for the removal
and replacement of this part.</notes>
</part>
On its own, an SGML or XML file (including HTML) doesn't do anything. It's a data format which just sits there until you run a program which does something with it