AS · Practice questions · Procedures and functions

Small parts, clear whole.

Six original Cambridge-style questions on procedures, functions and their terminology, with mark points.

Original questions All questions on this page are original work, written in the Cambridge AS & A Level style. They are not from past papers. They test the same concepts and skills the syllabus rewards.

Keep these straight

Statement or expression.

Procedure: PROCEDURE Name(...) ... ENDPROCEDURE; run with CALL Name(...).
Function: header ends RETURNS type; uses RETURN; used inside an expression, never with CALL.
Parameter is in the header; argument is in the call; they match in number, order and type.
Efficient: stop loops early, do not repeat calculations, replace copied code with a subroutine.

Recall

[3 marks]

Explain what is meant by each term: (a) parameter (b) argument (c) return value.

(a) An identifier in the procedure or function header that receives a value passed to the subroutine. ✓
(b) The actual value (or variable) passed to the subroutine when it is called. ✓
(c) The single value a function sends back to the calling code, which replaces the function call in the expression. ✓

Explain

[3 marks]

A large program is being written by a team. Explain three benefits of writing it as a set of procedures and functions.

Each subroutine can be written and tested separately, possibly by different programmers. ✓
Code that is needed in several places is written once and called many times, so the program is shorter. ✓
Maintenance is easier: a change or fix is made in one subroutine only; subroutines can also be reused in other programs (any three). ✓

Trace

[4 marks]

Study this function.

FUNCTION Mystery(N : INTEGER) RETURNS INTEGER
    DECLARE Result : INTEGER
    Result ← 0
    WHILE N > 0
        Result ← Result + (N MOD 10)
        N ← N DIV 10
    ENDWHILE
    RETURN Result
ENDFUNCTION

(a) Trace Mystery(4073). (b) State the output of OUTPUT Mystery(4073) * 2. (c) Describe the purpose of the function.

N 4073, Result 3; N 407, Result 10; N 40, Result 10; N 4, Result 14; N 0, loop ends. ✓
Mystery(4073) returns 14. ✓
(b) 14 * 2 = 28 is output. ✓
(c) It returns the sum of the digits of N. ✓

Write

[4 marks]

Write a function MaxOfThree that takes three integer parameters and returns the largest.

Header: FUNCTION MaxOfThree(A : INTEGER, B : INTEGER, C : INTEGER) RETURNS INTEGER. ✓
Max ← A, then IF B > Max THEN Max ← B ENDIF. ✓
IF C > Max THEN Max ← C ENDIF. ✓
RETURN Max and ENDFUNCTION. ✓

Write

[4 marks]

Write a procedure TimesTable that takes an integer parameter and outputs its multiplication table from 1 times to 12 times, one line each, for example 7 x 3 = 21. Then write a statement that uses it to output the 7 times table.

PROCEDURE TimesTable(Number : INTEGER) ... ENDPROCEDURE, with Count declared locally. ✓
FOR Count ← 1 TO 12 ... NEXT Count. ✓
OUTPUT Number, " x ", Count, " = ", Number * Count inside the loop. ✓
CALL TimesTable(7). ✓

Analysis

[3 marks]

A function checks whether a code is in an array of 500 codes. It uses a FOR loop from 1 to 500, sets Found ← TRUE when the code matches, and returns Found after the loop. Explain how the function could be made more efficient, and why this is better.

Use a conditional loop (WHILE / REPEAT) that stops when the code is found or the end of the array is reached, or RETURN TRUE as soon as a match is found. ✓
Fewer comparisons are made when the code is found early, for example 1 instead of 500 if it is the first element. ✓
So the function runs faster on average; it still returns FALSE after checking all 500 if the code is not there. ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.