Calling Procedures: Practice Questions (Computer Science Principles 3.12)

These are original Marlbridge practice questions, not past exam questions. All scenarios are fictional. The code is Marlbridge’s rendering of the exam reference notation (← assignment, = equality test, lists start at index 1, DISPLAY shows a value). Mark points are a suggested Marlbridge rubric, not an official scoring guideline. No calculator is needed or allowed. Try each question before opening its answer.

Question 1 (multiple choice · foundation)

In the procedure definition PROCEDURE total(a, b) and the call total(2, 5), which statement is correct?

(A) All four items are parameters.
(B) a and b are parameters; 2 and 5 are arguments.
(C) All four items are arguments.
(D) a and b are arguments; 2 and 5 are parameters.

Answer and explanation

Answer: (B). Parameters are the input variables in the definition; arguments are the values supplied in the call.

(A) and (C) ignore the distinction.
(D) reverses the terms.

Question 2 (multiple choice · core)

What is displayed?

PROCEDURE sq(n)
{
  RETURN(n * n)
}
DISPLAY(sq(sq(2)))

(A) 16
(B) 8
(C) Nothing is displayed.
(D) 4

Answer and explanation

Answer: (A). The inner call sq(2) returns 4; the outer call sq(4) returns 16.

(B) is 2 × 4.
(C) The outer DISPLAY shows the value returned.
(D) is only the inner call.

Question 3 (multiple choice · core)

The procedure diff(first, second) returns first - second. What does diff(4, 10) return?

PROCEDURE diff(first, second)
{
  RETURN(first - second)
}
DISPLAY(diff(4, 10))

(A) 14
(B) -6
(C) 40
(D) 6

Answer and explanation

Answer: (B). first is 4 and second is 10, so 4 − 10 = −6. Arguments are matched by position.

(A) adds the numbers.
(C) multiplies them.
(D) swaps the arguments.

Question 4 (multiple choice · core)

What is displayed?

PROCEDURE f(n)
{
  DISPLAY(n)
  RETURN(n + 1)
}
DISPLAY(f(7))

(A) 8
(B) 7 8
(C) 7
(D) 8 7

Answer and explanation

Answer: (B). f(7) runs first. Inside it DISPLAY(n) shows 7, then it returns 8. The outer DISPLAY then shows 8.

(A) ignores the display inside the procedure.
(C) ignores the outer display.
(D) reverses the order of events.

Question 5 (multiple choice · core)

What is displayed?

PROCEDURE g(n)
{
  IF(n < 0)
  {
    DISPLAY("ok")
    RETURN(0)
  }
  DISPLAY("done")
  RETURN(1)
}
x ← g(-1)

(A) done
(B) Nothing is displayed.
(C) ok done
(D) ok

Answer and explanation

Answer: (D). g(-1) takes the IF branch (n < 0), displays ok and returns at once. The line DISPLAY("done") after the return is never reached.

(A) is the display for a non-negative argument.
(B) The first DISPLAY runs.
(C) assumes code after RETURN still runs.

Question 6 (multiple choice · foundation)

The user types 7 when asked for input. What is displayed?

n ← INPUT()
DISPLAY(n * 2)

(A) Nothing is displayed.
(B) 7
(C) 14
(D) n

Answer and explanation

Answer: (C). INPUT() returns 7, which is stored in n; n * 2 is 14.

(A) The last line displays the value.
(B) forgets the doubling.
(D) n is a variable, not text.

Question 7 (multiple select, choose two · core)

Which two statements about procedures are true?

(A) RETURN ends the procedure immediately.
(B) A procedure runs as soon as it is defined.
(C) A call interrupts sequential execution; control returns to the point just after the call.
(D) Arguments are matched to parameters in any order.
(E) DISPLAY returns a value to the calling code.

Answer and explanation

Answers: (A) and (C). These are the basic rules of calls and returns.

(B) A procedure runs only when called.
(D) Arguments match parameters by position.
(E) DISPLAY shows a value; it does not return one.

Question 8 (constructed response · core)

(a) Write a procedure average(a, b) that returns the mean of its two parameters. (b) Write a statement that stores the average of 6 and 9 in m and displays it. (c) State what is displayed.

Answer and explanation

(a)

PROCEDURE average(a, b)
{
  RETURN((a + b) / 2)
}

(b)

m ← average(6, 9)
DISPLAY(m)

Suggested Marlbridge rubric (5 marks)

Mark point	Marks
(a) Procedure header with two parameters	1
(a) Returns (a + b) / 2 with correct brackets	1
(b) Calls with the arguments 6 and 9 and stores the result	1
(b) Displays `m`	1
(c) 7.5	1

Question 9 (constructed response · stretch)

The procedure lastItem(aList) returns the last element of a list, and firstItem(aList) returns the first. For nums equal to [4, 8, 15], trace DISPLAY(lastItem(nums) - firstItem(nums)), listing each call in the order it runs, with its returned value, and state the displayed result. Explain what would happen if lastItem were called with an empty list [].

Answer and explanation

PROCEDURE lastItem(aList)
{
  RETURN(aList[LENGTH(aList)])
}

PROCEDURE firstItem(aList)
{
  RETURN(aList[1])
}

Evaluation order (left to right): lastItem(nums): LENGTH(nums) is 3, so it returns nums[3], which is 15. Then firstItem(nums) returns nums[1], which is 4. The expression becomes 15 - 4 = 11, so 11 is displayed.

With an empty list, LENGTH is 0 and aList[0] is an invalid index, so an error message is produced and the program terminates.

Suggested Marlbridge rubric (5 marks)

Mark point	Marks
`lastItem(nums)` evaluated with LENGTH 3 and returns 15	1
`firstItem(nums)` returns 4	1
Combines the returned values: 15 − 4	1
Displays 11	1
Explains the error for an empty list (index 0 is invalid)	1

How did you do?

Count the questions you got right first time, then read the explanation for every one you missed, including the wrong options you rejected correctly, because the distractors show you the typical slips. Anything you missed twice goes onto your revision list for the revision notes; re-read the matching section of the study guide before trying again.