A-LevelComputer ScienceProgramming9618/22 · May/June 2021 · Q515 Marks

A student is learning about arrays. She wants to write a program to: • declare a 1D array RNum of 100 elements of type INTEGER • assign each element a random value in the range 1 to 200 inclusive • count and output how many numbers generated were between 66 and 173 inclusive.

(a)(i)Write pseudocode to represent the algorithm.[6]
(a)(ii)The student decides to modify the algorithm so that each element of the array will contain a unique value. Describe the changes that the student needs to make to the algorithm.[3]
(b)(i)The following is a pseudocode function. Line numbers are given for reference only. 01 FUNCTION StringClean(InString : STRING) RETURNS STRING 02 03 DECLARE NextChar : CHAR 04 DECLARE OutString : STRING 05 DECLARE Counter : INTEGER 06 07 OutString ← "" 08 09 FOR Counter ← 1 TO LENGTH(InString) 10 NextChar ← MID(InString, Counter, 1) 11 NextChar ← LCASE(NextChar) 12 IF NOT((NextChar < 'a') OR (NextChar > 'z')) THEN 13 OutString ← OutString & NextChar 14 ENDIF 15 NEXT Counter 16 17 RETURN OutString 18 19 ENDFUNCTION Examine the pseudocode and complete the following table. Give a line number containing an example of an initialisation statement. Give a line number containing the start of a repeating block of code. Give a line number containing a logic operation. Give the number of parameters to the function MID().[4]
(b)(ii)Write a simplified version of the statement in line 12.[2]

Mark scheme

Marking points from the official mark scheme (May/June 2021). The mark or mark type is shown in brackets.

[1] (a)(i) DECLARE RNum : ARRAY [1:100] OF INTEGER
[1] (a)(i) DECLARE Index, Count : INTEGER
[1] (a)(i) Count ← 0
[1] (a)(i) FOR Index ← 1 TO 100
[1] (a)(i) RNum[Index] ← INT(RAND(200)) + 1
[1] (a)(i) IF RNum[Index] >= 66 AND RNum[Index] <= 173 THEN
[1] (a)(i) Count ← Count + 1
[1] (a)(i) ENDIF
[1] (a)(i) NEXT Index
[1] (a)(i) OUTPUT Count
[1] (a)(ii) Initialise the array to a rogue value (to indicate 'unassigned' element)
[1] (a)(ii) Add a conditional loop to:
[1] (a)(ii) Generate and store a random number (in the correct range)
[1] (a)(ii) Check the stored number against values already in the array
[1] (a)(ii) If the stored number is found then generate another random value
[1] (a)(ii) Otherwise add it to the array (and exit loop)
[1] (b)(i) Give a line number containing an example of an initialisation statement.: 07
[1] (b)(i) Give a line number containing the start of a repeating block of code.: 09 / 10
[1] (b)(i) Give a line number containing a logic operation.: 12
[1] (b)(i) Give the number of parameters of function MID().: 3
[1] (b)(ii) IF (NextChar >= 'a') AND (NextChar <= 'z') THEN
[1] (b)(ii) One mark for IF ... AND ...
[1] (b)(ii) One mark for both conditions

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