Parse a C program using compiler tools - Lex, YACC, Flex, Bison?

What is the criteria that the program will use to determine that one or two lines of C will translate into multiple *files* in PHP? This is the part of your question that really throws me for a loop. A program can only do something that you can explain how to do yourself. So explain it, in plain english, how you would look at a C program and decide, "ah, that's three PHP files right there."