A-LevelComputer ScienceProgramming9618/23 · May/June 2025 · Q58 Marks

A module Parity() takes a string as a parameter. The parameter has the identifier BitString and it represents a binary value. The module will concatenate a single character to the end of BitString by applying one of the two rules: : '0' if Bitstring contains an even number of 1s : '1' if Bitstring contains an odd number of 1s. The modified value of BitString is then returned. For example: Parameter String returned Explanation "0010010110" "00100101100" there are an even number of 1s in the string passed to Parity() so a '0' is concatenated to the end of BitString "101010" "1010101" there are an odd number of 1s in the string passed to Parity() so a '1' is concatenated to the end of BitString Write pseudocode for the module Parity() Assume the parameter BitString can only contain the characters '0' and '1'

Write pseudocode for the module Parity() Assume the parameter BitString can only contain the characters '0' and '1'[8]

Mark scheme

Marking points from the official mark scheme (May/June 2025). The mark or mark type is shown in brackets.

[8] Example solution: FUNCTION Parity(BitString : STRING) RETURNS STRING DECLARE Index, Count: INTEGER Count <- 0 FOR Index <- 1 TO LENGTH(BitString) IF MID(BitString, Index, 1) = '1' THEN Count <- Count + 1 ENDIF NEXT Index IF Count MOD 2 = 1 THEN BitString <- BitString & '1' ELSE BitString <- BitString & '0' ENDIF RETURN BitString ENDFUNCTION
MP1 Function heading and ending and parameter (STRING) and return type STRING
MP2 Loop for length of BitString
MP3 Extract current character in a loop
MP4 Compare current character to '1' or '0' in a loop
MP5 Increment count and was Initialised earlier in a loop
MP6 Check if even/odd number of 1s
MP7 Append '1' or '0' as appropriate
MP8 Return amended BitString

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