Keeping track on index in XSLT/updating variables in XSLT.

I am programming in XML/XSLT. I need to create an XSLT program which generates a header file which are to be used as initialization data for a C program. The initialization includes initialization of an array and therefore I need to keep track on the index of the array so I know the current first free location in the array. Since XSLT does not support updating variables I can not figure out how to keep track on this index.

Can anybody help me ?!