CS314
Assignment 4
1 Syntax Directed Translation
Modify the recursive descent parser in Homework 3 (sample solution is posted
in Sakai) such that it prints the number of assignment statements in the
input program after it successfully parsed the program, and the number of
addition operations. For the program listed below, your parser should print
“3 assignments, 4 addition operations”.
def g(a, b):
a = 2 + b
if a <= b + 1: b = a + 1
else: b = a + 1
return b
2 Problem — Pointers
Given the following correct program in C,
(a) give the correct type definitions for pointer variables ra, rb, rc,
rra, rrb, and rrc.
(b) draw a picture that shows all of the variables and their contents similar
to the diagram in lecture 10. Your picture should show the variables
and their values just before the first print statement (*).
(c) show the output from this program.
(d) write a statement involving a pointer expression using the variables in
this program which is ILLEGAL given your declared types.
main() {int a, b, c;
??? ra; ??? rb; ??? rc; ??? rra; ??? rrb; ??? rrc;
1
a = 1; b = 2; c = 3;
ra = &a;
rb = &b;
rc = &c;
ra = rb;
rra = &rb;
rc = *rra;
rrc = rra;
rc = &a;
rrb = &rc;
rb = &c;
*ra = 4;
*rb = *ra + 5;
/* (*) */
printf ("%d %d %d\n",a,b,c);
printf("%d %d\n",*ra,*rb);
printf("%d %d %d\n",**rra,**rrb,**rrc);
}
3 Problem — Freeing Memory
Here is a code fragment from our singly-linked list example from class.
/* DEALLOCATE LIST */
for (current_cell = head;
current_cell != NULL;
current_cell = current_cell-next)
free(current_cell);
How can you rewrite this code to make it safe? You can introduce new
variables, if needed.
2
