>#include <stdio.h> >#define yell(i,l,o,v,e,u) o##v##i##l defines a macro called yell. The preprocessor operator ## concatenates it's operands together so som

>#include <stdio.h> >#define yell(i,l,o,v,e,u) o##v##i##l defines a macro called yell. The preprocessor operator ## concatenates it's operands together so something like ma##in gets transformed into main. >#define billy_bob yell(i,n,m,a,t,e) defines a macro called billy_bob that simply expands to the macro yell. When we call yell with the given arguments we get m##a##i##n (look at the order of the arguments for yell) which gets transformed into main. >billy_bob() Expanding the macro turns this line into main(). >{ > printf("no main in da house!"); >} So now we've declared a main function that just prints "no main in da house!".