Homework Assignment #3 Solutions
CSE 452: Fall 2004
Due: 09/30/04
Textbook Evaluations: Please complete and turn-in your evaluations of
Chapter 3 by the due date shown above. Evaluations should be emailed to
cse452@cse.msu.edu and should include your name (preferably as part of
evaluation file name). Please be sure to give concrete examples of
improvements to be made when you are not satisfied with a specific part of the
chapter.
Instructions: Answer each question below. Your answers must be generated
using a common word processing program such as MS Word or LaTex
(handwritten work will not be accepted). Figures may be hand-drawn or you
may generate these using a graphics package such as XFig. Hand in all answers
in hardcopy form (no emails) by the due date shown.
1. Taking into account what you should now know about scoping and
declaration orders from Chapter 3, consider the following C program:
void fun(void) {
int a, b, c; /* definition 1*/
…
while (…) {
int b, c, d; /* definition 2 */
…
<===============
while (…) {
int c, d, e; /* definition 3 */
…
<===============
}
…
<===============
}
…
<===============
}
1
2
3
4
For each of the four marked points in this function, list each visible variable,
along with the number of the definition statement that defines it.
1.
a – definition 1
b, c, d – definition 2
2.
a – definition 1
b – definition 2
c, d, e – definition 3
3.
Same as point #1 above.
4.
a, b, c – definition 1
2. Consider the following skeletal program:
procedure Main is
X, Y, Z : Integer;
procedure Sub1 is
A, Y, Z : Integer;
begin -- of Sub1
…
end -- of Sub1
procedure Sub2 is
A, B, Z : Integer;
begin -- of Sub2
…
end -- of Sub2
procedure Sub3 is
A, X, W : Integer;
begin -- of Sub3
…
end -- of Sub3
begin -- of Main
…
end -- of Main
Given the following calling sequences and assuming that dynamic scoping
is used, what variables are visible during the execution of the last
subprogram activated? Include with each visible variable the name of the
unit where it is declared.
(a)
(b)
Variable
a, x, w
b, z
y
Where Declared
sub3
sub2
sub1
a, y, z
sub1
(c)
x, w
b
sub3
sub2
a, y, z
x, w
sub1
sub3
3. Briefly describe the difference between a declaration and a definition and why
the distinction between the two is important.
A declaration introduces a name and indicates its scope, whereas a definition
describes the thing to which the declared name is bound. A declaration may not
be complete enough to be a definition and as such a separate definition must be
included somewhere within the scope of that name in order for it to be used.
Thus, a declaration may or may not contain information which defines what is
bound to a given name (function or variable).