| (a) |
What is the effect of adding the keyword static
to a local varibale in a procedure? |
[2] |
|
- the variable retains its value between
function calls (1 mark),
- and exists throughout the lifetime of
the program execution (1 mark).
|
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| (b) |
Describe the difference between
call-by-reference and call-by-value parameter passing in C. |
[4] |
|
- If a formal parameter of a function or
procedure is passed via a call-by-reference parameter passing scheme, then any changes to
that variable during the lifetime of the procedure, invocation will carry through after
the procedure has returned (2 marks).
- In contrast, changes to variables
which are passed using the call-by-value scheme are only retained during the lifetime of
the procedure/function invocation (2 marks).
- call-by-reference parameter passing is
achieved in C by using pointers as the formal arguments to functions (2 marks)
- 2 marks for each point above, to a
maximum of four marks.
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| (c) |
Find the eight syntax errors in the
following fragment of code: include
<stdio.h>
void func(int x[], int y)
main() {
int a(5), b, i;
for (i=0;i<5,i++) a[i] = 2*1;
b==16;
for(i=0;i<5;i++) printf("%d\n,a[i]);
return;
}
void func(int x[], int y);
{
integer i;
for(i=0;i<5;i++) {
x[i]+=2;
y+=2;
}
|
[8] |
|
include <stdio.h>
/* missing # 1 mark */ void func(int
x[], int y) /* missing ; 1 mark */
main() {
/* ok missing void(s) 0 marks */
int a(5), b, i;
/* (5) should be [5] 1 mark */
for (i=0;i<5,i++) a[i] = 2*1; /* last, should be ; 1 mark */
b==16;
/* ok null statement, 0 mark */
for(i=0;i<5;i++) printf("%d\n,a[i]); /* missing " 1 mark */
return;
/* ok return, 0 mark */
}
void func(int x[], int y); /* extra ; 1 mark */
{
integer i; /* integer should be int 1 mark */
for(i=0;i<5;i++) { /* no close } 1 mark */
x[i]+=2;
y+=2;
/* ok missing return 0 marks */
} |
|
| (d) |
Write a function that prompts the
user to enter a number in the range 0-4. If the number entered is outside the required
range, a prompt for user input should be repeated; otherwise the function returns the
integer selected by the user. |
[6] |
|
A definition
of the function menu (the students may have used an alternative function name) follows: int menu() {
int i=-1;
while (i<0 ||
i>4) {
printf("Enter a digit in the range
0--4?");
scanf("%d", &i);
}
return i;
}
an alternative definition that uses a
do-while is shown below:
int menu() {
int i;
do {
printf("Enter a digit in the range
0--4?");
scanf("%d", &i);
} while (i<0 || i>4)
return i;
}
and use the following marking scheme
should be used for either solutions:
- one mark for a correct procedure
definition.
- one mark for using an iteration
statement.
- two mark for repeatedly iterating
while the entered value is not in the range 0-4. i.e., one mark for the expressions i<0
and i>4, and one mark for the use of ||. Alteratively, the students may have used
(i>=0 && i<=4), which should also be awarded two marks.
- one mark for printing a prompt (any
text will do) with printf.
- one mark for using scanf to read in a
digit.
- no marks should be deducted for
trivial syntactic errors.
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