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Computer Science · May / June 2023 · Paper 22 · Question 7

0478

As printed in the paper

The question as text

An algorithm has been written in pseudocode to calculate a check digit for a four-digit number. The algorithm then outputs the five-digit number including the check digit. The algorithm stops when –1 is input as the fourth digit. 01 Flag FALSE 02 REPEAT 03 Total 0 04 FOR Counter 1 TO 4 05 OUTPUT "Enter a digit ", Counter 06 INPUT Number[Counter] 07 Total Total + Number * Counter 08 IF Number[Counter] = 0 09 THEN 10 Flag TRUE 11 ENDIF 12 NEXT Counter 13 IF NOT Flag 14 THEN 15 Number[5] MOD(Total, 10) 16 FOR Counter 0 TO 5 17 OUTPUT Number[Counter] 18 NEXT 19 ENDIF 20 UNTIL Flag

Read automatically from the paper; the printed page above is exact.

Show the answer and mark scheme

  • 7(a)[3]

    07
    04/12 or 16/18
    02/20

  • 7(b)[3]

    One mark for each error identified and correction

    Line 07 Total ← Total + Number * Counter

    should be Total ← Total + Number[Counter] * Counter

    Line 08 IF Number[Counter] = 0

    should be IF Number[Counter] = -1 // should be IF Number[Counter] < 0

    Line 16 FOR Counter ← 0 TO 5

    should be FOR Counter ← 1 TO 5

  • 7(c)[4]

    One mark for place in algorithm (max one)

    around lines 05 and 06
    line 07
    (immediately) after the input of the number

    Three marks pseudocode

    One mark for each point (max three)

    Use of REPEAT … UNTIL // any working loop structure
    check for >0 // >=0
    check for <10 // >9
    check for whole number
    check for -1
    check for length of digit <> 1

    Example

    REPEAT

    OUTPUT "Enter a digit "

    INPUT Number[Counter]

    UNTIL Number[Counter] = Round(Number[Counter],0) AND ((Number[Counter] = -1) OR

    (Number[Counter] > 0 AND Number[Counter] < 10))

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