2.2.1 Programming Techniques Exam Questions

Past paper questions

1. Question 1H446/021 mark

   Line 06 of a pseudocode program is: first = int(first). The variable first holds a value that the user has typed in. State the purpose of line 06.

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   Converts the string to an integer / casts to integer / type conversion from string to int (1 mark)

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   01/ 1
2. Question 2H446/024 marks

   Describe one benefit and one drawback of using global variables instead of parameter passing in a subroutine.

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   Benefit: Can be accessed anywhere / No need to pass as parameter / Simpler function calls / Maintains state Drawback: Can be changed unintentionally / Harder to debug / Creates dependencies / Reduces modularity / Not thread-safe (4 marks - 2 per point)

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   01234/ 4
3. Question 3H446/02 · June 20242 marks

   Describe what is meant by a variable.

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   A named location in memory / Stores a value that can change during program execution / Has an identifier and a value / Can be read from and written to (2 marks)

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   012/ 2
4. Question 4H446/02 · June 20241 mark

   A student has written this pseudocode algorithm. Give the identifiers of all the variables used in this program.

   01 a = 12
   02 do
   03 b = input("Enter a number")
   04 until b >= 0 and b <= 100
   05 for c = 1 to a
   06 print(c * a)
   07 next c

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   a, b, c (1 mark - all three needed)

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   01/ 1
5. Question 5H446/02 · June 20242 marks

   Describe the difference between a do loop and a while loop.

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   Do loop: executes at least once, condition checked at end / While loop: condition checked at start, may not execute at all / Do loop is post-condition, while is pre-condition (2 marks)

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6. Question 6H446/029 marks

   Compare the use of variables and parameters in a treasure-hunting game. Include: local and global variables, how they can be used, passing parameters by value and by reference.

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   Levels of response (9 marks) Local: exists only within subroutine, destroyed when subroutine ends Global: accessible throughout program, persists for program lifetime Use: Board could be global (accessed everywhere), score local to display function By value: copy made, original unchanged, safe for read-only By reference: pointer to original, changes affect original, needed for updates

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   0123456789/ 9
7. Question 7H446/022 marks

   A function isInteger(number) takes a string and checks that every character is a digit by comparing ASCII values inside a loop that uses count as the index. Write the condition, using asc(), that is true when the character number[count] is not a digit from 0 to 9.

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   if asc(number[count]) < 48 OR asc(number[count]) > 57 then or equivalent checking ASCII values 48-57 (2 marks)

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8. Question 8Practice question · H446/02 style4 marks

   Write a recursive function factorial(n) that returns n! for a positive integer n, and identify the base case.

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   • function factorial(n) header with correct parameter • Base case: if n == 1 (or n == 0) then return 1 • Recursive call: return n * factorial(n - 1) • Correct structure / endfunction, with the base case reached before the recursive case Example: function factorial(n) if n <= 1 then return 1 else return n * factorial(n - 1) endif endfunction (4 marks – 1 per point)

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9. Question 9Practice question · H446/02 style3 marks

   Explain the difference between passing a parameter by value and passing it by reference. Give one situation in which passing by reference is preferable.

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   • By value: a copy of the data is passed, so changes made inside the subroutine do not affect the original variable • By reference: the address of the variable is passed, so changes inside the subroutine change the original variable • Preferable when a large data structure would be slow or memory-hungry to copy, or when the subroutine must update the caller's variable (e.g. a procedure that sorts an array in place) (3 marks – 1 per point)

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