C and UNIX Q's?

HI, i have some questions to ask about C and UNIX programming..

a) If an error/exception arising in one function is to be handled in another function some levels back in the calling sequence, what operations need to be performed on the run-time stack?

Does C provide a direct mechanism for this sort of error handling? Explain how the functions setjmp()/longjmp() might be used to achieve a similar effect?

b) Why is dynamic memory needed in general for module implementation? Explain the importance of pointers in connection with your answer.

Kind regards,
Atif.