Programming Practice: Writing and Refining Programs - Worksheets, Questions and Revision

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GCSE · Programming

P2.7 Programming Practice: Writing and Refining Programs

OCR J277 · Calculators not allowed · about 135 minutes

Total Marks

Name: _______________________________ Date: ____ / ____ / ______

Answer ALL questions. Show all your working.

A program should input a whole number and output whether it is odd or even.

Write an algorithm that inputs an integer and outputs "Even" if the number is exactly divisible by 2, or "Odd" otherwise.

(a)A program should input a whole number and output whether it is odd or even.

Write an algorithm that inputs an integer and outputs "Even" if the number is exactly divisible by 2, or "Odd" otherwise.(3)

(Total for Question 1 is 3 marks)

Write an algorithm, using a count-controlled loop, that outputs the sum of the whole numbers from 1 to 20 inclusive.

(a)Write an algorithm, using a count-controlled loop, that outputs the sum of the whole numbers from 1 to 20 inclusive.(3)

(Total for Question 2 is 3 marks)

A string variable is set as: name = "Aditi"

(a)A string variable is set as:
name = "Aditi"

State the value of LEN(name).(1)

(b)Write one line of code that outputs the first three characters of name, using SUBSTRING(startIndex, numberOfChars, string).(2)

(Total for Question 3 is 3 marks)

A simple program advises drivers based on a temperature reading (in degrees Celsius). Write an algorithm that inputs a temperature and outputs:
- "Ice warning" if the temperature is less than or equal to 0
- "Mild" if the temperature is greater than 0 and less than 20
- "Warm" if the temperature is 20 or greater

(a)A simple program advises drivers based on a temperature reading (in degrees Celsius). Write an algorithm that inputs a temperature and outputs:
- "Ice warning" if the temperature is less than or equal to 0
- "Mild" if the temperature is greater than 0 and less than 20
- "Warm" if the temperature is 20 or greater(4)

(Total for Question 4 is 4 marks)

An array called scores stores the test scores of 8 students:
scores = [56, 78, 45, 90, 33, 67, 82, 71]

Write an algorithm that uses iteration to calculate and output the average score of the class.

(a)An array called scores stores the test scores of 8 students:
scores = [56, 78, 45, 90, 33, 67, 82, 71]

Write an algorithm that uses iteration to calculate and output the average score of the class.(5)

(Total for Question 5 is 5 marks)

Write an algorithm that repeatedly asks the user to input a whole number between 1 and 10 (inclusive), rejecting any input outside this range, until a valid number is entered. The algorithm should then output the valid number.

(a)Write an algorithm that repeatedly asks the user to input a whole number between 1 and 10 (inclusive), rejecting any input outside this range, until a valid number is entered. The algorithm should then output the valid number.(4)

(Total for Question 6 is 4 marks)

Write a function called applyDiscount that takes two parameters, price (a real number, in pounds) and percentageOff (an integer), and returns the price after the percentage discount has been subtracted.

(a)Write a function called applyDiscount that takes two parameters, price (a real number, in pounds) and percentageOff (an integer), and returns the price after the percentage discount has been subtracted.(4)

(Total for Question 7 is 4 marks)

A student has written the following algorithm, which is intended to output the numbers 1 to 5, but it only outputs 1 to 4:

total = 0
FOR i = 1 TO 4
    OUTPUT i
NEXT i

(a)A student has written the following algorithm, which is intended to output the numbers 1 to 5, but it only outputs 1 to 4:

total = 0
FOR i = 1 TO 4
    OUTPUT i
NEXT i

Identify the error in the algorithm.(1)

(b)Write the corrected FOR loop line so that the algorithm outputs 1 to 5.(2)

(Total for Question 8 is 3 marks)

An array called names stores the names of students in a class:
names = ["Priya", "Oliver", "Fatima", "Callum", "Grace"]

Write a function called findStudent that takes the array names and a string searchName as parameters, and returns the index of searchName in the array if found, or -1 if the name is not found.

(a)An array called names stores the names of students in a class:
names = ["Priya", "Oliver", "Fatima", "Callum", "Grace"]

Write a function called findStudent that takes the array names and a string searchName as parameters, and returns the index of searchName in the array if found, or -1 if the name is not found.(5)

(Total for Question 9 is 5 marks)

Write a function called countVowels that takes a string parameter word and returns the number of vowels (a, e, i, o, u) in the string, ignoring case.

(a)Write a function called countVowels that takes a string parameter word and returns the number of vowels (a, e, i, o, u) in the string, ignoring case.(5)

(Total for Question 10 is 5 marks)

A text file called "attendance.txt" contains one student name per line. Write an algorithm that opens the file, reads every line until the end of the file, and outputs the total number of names in the file.

(a)A text file called "attendance.txt" contains one student name per line. Write an algorithm that opens the file, reads every line until the end of the file, and outputs the total number of names in the file.(4)

(Total for Question 11 is 4 marks)

Write an algorithm that outputs the numbers 1 to 30. For multiples of 3, output "Fizz" instead of the number. For multiples of 5, output "Buzz" instead of the number. For multiples of both 3 and 5, output "FizzBuzz" instead of the number.

(a)Write an algorithm that outputs the numbers 1 to 30. For multiples of 3, output "Fizz" instead of the number. For multiples of 5, output "Buzz" instead of the number. For multiples of both 3 and 5, output "FizzBuzz" instead of the number.(5)

(Total for Question 12 is 5 marks)

A function is intended to return the total of all the numbers in an array called numbers, but it returns an incorrect result:

FUNCTION calculateTotal(numbers)
    total = 0
    FOR i = 1 TO LEN(numbers)
        total = total + numbers[i]
    NEXT i
    RETURN total
ENDFUNCTION

(a)A function is intended to return the total of all the numbers in an array called numbers, but it returns an incorrect result:

FUNCTION calculateTotal(numbers)
    total = 0
    FOR i = 1 TO LEN(numbers)
        total = total + numbers[i]
    NEXT i
    RETURN total
ENDFUNCTION

The array is 0-indexed, so a 5-element array has valid indices 0 to 4.

Identify the error in the function.(1)

(b)Rewrite the FOR loop line so that the function works correctly.(2)

(Total for Question 13 is 3 marks)

A 2D array called grid stores temperature readings (in degrees Celsius) for a 3 by 3 grid of sensors, accessed using grid[row, column], with rows and columns numbered 0 to 2.

Write an algorithm that uses nested iteration to calculate and output the total of all 9 readings in the grid.

(a)A 2D array called grid stores temperature readings (in degrees Celsius) for a 3 by 3 grid of sensors, accessed using grid[row, column], with rows and columns numbered 0 to 2.

Write an algorithm that uses nested iteration to calculate and output the total of all 9 readings in the grid.(5)

(Total for Question 14 is 5 marks)

Write a function called findMax that takes an array of integers, values, as a parameter and returns the largest value in the array. You may assume the array contains at least one element.

(a)Write a function called findMax that takes an array of integers, values, as a parameter and returns the largest value in the array. You may assume the array contains at least one element.(5)

(Total for Question 15 is 5 marks)

A text file called "results.txt" contains one exam mark (an integer out of 100) per line, for every student in a class. Write an algorithm that reads every mark from "results.txt", and writes only the marks that are 40 or above to a new file called "pass.txt", with one mark per line. The algorithm should output the total number of passing marks written.

(a)A text file called "results.txt" contains one exam mark (an integer out of 100) per line, for every student in a class. Write an algorithm that reads every mark from "results.txt", and writes only the marks that are 40 or above to a new file called "pass.txt", with one mark per line. The algorithm should output the total number of passing marks written.(6)

(Total for Question 16 is 6 marks)

Write a function called isValidPassword that takes a string parameter password and returns a Boolean: True if the password is at least 8 characters long AND contains at least one digit (0-9), or False otherwise.

(a)Write a function called isValidPassword that takes a string parameter password and returns a Boolean: True if the password is at least 8 characters long AND contains at least one digit (0-9), or False otherwise.(6)

(Total for Question 17 is 6 marks)

A student has written the following function, intended to search for a value target in an array numbers and return its index, or -1 if not found. When tested, the function sometimes returns the wrong result:

FUNCTION search(numbers, target)
    FOR i = 0 TO LEN(numbers) - 1
        IF numbers[i] == target THEN
            found = i
        ELSE
            found = -1
        ENDIF
    NEXT i
    RETURN found
ENDFUNCTION

(a)A student has written the following function, intended to search for a value target in an array numbers and return its index, or -1 if not found. When tested, the function sometimes returns the wrong result:

FUNCTION search(numbers, target)
    FOR i = 0 TO LEN(numbers) - 1
        IF numbers[i] == target THEN
            found = i
        ELSE
            found = -1
        ENDIF
    NEXT i
    RETURN found
ENDFUNCTION

Identify why this function does not always work correctly, using an example to support your answer.(2)

(b)Rewrite the function so that it works correctly for every case.(3)

(Total for Question 18 is 5 marks)

A shop stores its stock data in a text file called "stock.txt". The file lists each item on its own line, followed immediately by its quantity on the next line, repeated for every item, for example:
Kettle
14
Toaster
3

Write a program that:
- reads all the stock data from "stock.txt" into two parallel arrays, itemNames and quantities, keeping track of how many items were read in a variable itemCount
- includes a function called findItem that takes itemNames, itemCount and a search name as parameters, and returns the index of the item, or -1 if not found
- asks the user to input an item name to check
- uses findItem to look up the item and outputs its quantity, or a suitable message if the item is not found
- if the item is found and its quantity is less than 5, additionally outputs a low stock warning

(a)A shop stores its stock data in a text file called "stock.txt". The file lists each item on its own line, followed immediately by its quantity on the next line, repeated for every item, for example:
Kettle
14
Toaster
3

Write a program that:
- reads all the stock data from "stock.txt" into two parallel arrays, itemNames and quantities, keeping track of how many items were read in a variable itemCount
- includes a function called findItem that takes itemNames, itemCount and a search name as parameters, and returns the index of the item, or -1 if not found
- asks the user to input an item name to check
- uses findItem to look up the item and outputs its quantity, or a suitable message if the item is not found
- if the item is found and its quantity is less than 5, additionally outputs a low stock warning(8)

(Total for Question 19 is 8 marks)

A student has written the following program, which is intended to calculate and output the average of a set of numbers entered by the user. The user enters -1 to stop entering numbers. However, the program does not work correctly if a negative number (other than -1) is entered by mistake, and it does not handle the case where no valid numbers are entered at all:

total = 0
count = 0
INPUT number
WHILE number != -1
    total = total + number
    count = count + 1
    INPUT number
ENDWHILE
average = total / count
OUTPUT average

(a)A student has written the following program, which is intended to calculate and output the average of a set of numbers entered by the user. The user enters -1 to stop entering numbers. However, the program does not work correctly if a negative number (other than -1) is entered by mistake, and it does not handle the case where no valid numbers are entered at all:

total = 0
count = 0
INPUT number
WHILE number != -1
    total = total + number
    count = count + 1
    INPUT number
ENDWHILE
average = total / count
OUTPUT average

Explain one weakness of this program, other than the lack of comments, referring to what happens if the user enters -1 as their very first input.(2)

(b)Refine the program so that: any negative number entered (not just -1) ends the input phase in the same way as -1, and the program outputs a suitable message instead of calculating an average if no valid numbers were entered.(4)

(Total for Question 20 is 6 marks)

Mark scheme · P2.7 Programming Practice: Writing and Refining Programs

Question 1

(a) B1 INPUT statement storing the number in a suitably named variable (oe)
(a) B1 correct selection using MOD 2 == 0 (or an equivalent DIV-based test) as the condition
(a) B1 correct OUTPUT of "Even" and "Odd" in the correct branches (oe; ignore minor syntax, accept any equivalent selection structure)

(a) Answer:

INPUT number
IF number MOD 2 == 0 THEN
    OUTPUT "Even"
ELSE
    OUTPUT "Odd"
ENDIF

Question 2

(a) B1 a total (accumulator) variable initialised to 0 before the loop
(a) B1 correct FOR loop from 1 TO 20 that adds the loop counter to the total on each iteration
(a) B1 OUTPUT of the total placed after the loop has finished (oe)

(a) Answer:

total = 0
FOR i = 1 TO 20
    total = total + i
NEXT i
OUTPUT total

Question 3

(a) B1 5
(a) Answer: 5
(b) B1 correct OUTPUT statement calling SUBSTRING with name as the string argument
(b) B1 correct start index and length arguments that return the first three characters (oe; accept either a 0-indexed or 1-indexed convention provided the result is the first three characters)
(b) Answer: OUTPUT SUBSTRING(0, 3, name)

Question 4

(a) B1 INPUT statement storing the temperature
(a) B1 correct condition and output for the "Ice warning" branch (temperature ≤ 0)
(a) B1 correct condition and output for the "Warm" branch (temperature ≥ 20), using a nested/ELSE IF selection structure
(a) B1 correct output for "Mild" as the remaining case, with all three outcomes mutually exclusive (oe; accept any correctly ordered nested selection)

(a) Answer:

INPUT temperature
IF temperature <= 0 THEN
    OUTPUT "Ice warning"
ELSE
    IF temperature < 20 THEN
        OUTPUT "Mild"
    ELSE
        OUTPUT "Warm"
    ENDIF
ENDIF

Question 5

(a) B1 a total variable initialised to 0 before the loop
(a) B1 correct count-controlled loop that iterates over every element of the array (indices 0 to 7, or equivalent)
(a) B1 correct accumulation, total = total + scores[i], inside the loop
(a) B1 correct division of the total by 8 (the number of elements) after the loop, to calculate the average
(a) B1 OUTPUT of the average value

(a) Answer:

scores = [56, 78, 45, 90, 33, 67, 82, 71]
total = 0
FOR i = 0 TO 7
    total = total + scores[i]
NEXT i
average = total / 8
OUTPUT average

Question 6

(a) B1 correct condition-controlled loop structure with the exit-check after the input (e.g. REPEAT...UNTIL), or an equivalent entry-check loop that repeats correctly
(a) B1 INPUT statement placed inside the loop
(a) B1 correct UNTIL/loop condition testing number ≥ 1 AND number ≤ 10 (oe)
(a) B1 OUTPUT of the valid number placed after the loop has ended

(a) Answer:

REPEAT
    INPUT number
UNTIL number >= 1 AND number <= 10
OUTPUT number

Question 7

(a) B1 correct FUNCTION header with two parameters, e.g. FUNCTION applyDiscount(price, percentageOff)
(a) B1 correct calculation of the discount amount, e.g. discount = price * percentageOff / 100 (oe)
(a) B1 correct calculation of the new price by subtracting the discount from the original price (oe)
(a) B1 correct RETURN of the new price, with the function correctly closed using ENDFUNCTION (any correct logic; ignore minor syntax)

(a) Answer:

FUNCTION applyDiscount(price, percentageOff)
    discount = price * percentageOff / 100
    newPrice = price - discount
    RETURN newPrice
ENDFUNCTION

Question 8

(a) B1 identifies that the loop's upper bound is set to 4 instead of 5, so the loop only executes for i = 1, 2, 3, 4 and misses 5 (oe, must reference the incorrect bound value)
(a) Answer: The FOR loop's upper bound is set to 4 instead of 5, so it only outputs 1, 2, 3 and 4, and stops before it can output 5.
(b) B1 correct corrected FOR loop line: FOR i = 1 TO 5
(b) B1 the rest of the algorithm (NEXT i and OUTPUT i) is left unchanged and still functionally correct
(b) Answer: FOR i = 1 TO 5

Question 9

(a) B1 correct FUNCTION header taking both the array and the search name as parameters, e.g. FUNCTION findStudent(names, searchName)
(a) B1 correct iteration through every index of the array (e.g. FOR i = 0 TO LEN(names) - 1, oe)
(a) B1 correct selection comparing the current array element to searchName, e.g. IF names[i] == searchName THEN
(a) B1 correct RETURN of the current index i inside the loop when a match is found
(a) B1 correct RETURN of -1 placed after the loop, only reached when no match has been found

(a) Answer:

FUNCTION findStudent(names, searchName)
    FOR i = 0 TO LEN(names) - 1
        IF names[i] == searchName THEN
            RETURN i
        ENDIF
    NEXT i
    RETURN -1
ENDFUNCTION

Question 10

(a) B1 correct FUNCTION header with one string parameter, e.g. FUNCTION countVowels(word)
(a) B1 a count variable initialised to 0 before iterating
(a) B1 correct iteration through every character of the string (e.g. FOR i = 0 TO LEN(word) - 1, oe) using a case-conversion function so case is ignored
(a) B1 correct selection testing the current character against the five vowels, combined with OR, and incrementing count when true
(a) B1 correct RETURN of count after the loop has ended

(a) Answer:

FUNCTION countVowels(word)
    count = 0
    FOR i = 0 TO LEN(word) - 1
        letter = UPPER(SUBSTRING(i, 1, word))
        IF letter == "A" OR letter == "E" OR letter == "I" OR letter == "O" OR letter == "U" THEN
            count = count + 1
        ENDIF
    NEXT i
    RETURN count
ENDFUNCTION

Question 11

(a) B1 correct file opened for reading, e.g. myFile = OPENFILE("attendance.txt", READ)
(a) B1 a count variable initialised to 0 before the loop
(a) B1 correct condition-controlled loop that continues WHILE NOT EOF(myFile), reading a line with READFILE(myFile) and incrementing count on each iteration
(a) B1 OUTPUT of count placed after the loop, with the file closed using CLOSEFILE(myFile) (oe; accept the close statement in either position relative to the output)

(a) Answer:

myFile = OPENFILE("attendance.txt", READ)
count = 0
WHILE NOT EOF(myFile)
    line = READFILE(myFile)
    count = count + 1
ENDWHILE

CLOSEFILE(myFile)

OUTPUT count

Question 12

(a) B1 correct FOR loop from 1 to 30
(a) B1 correct condition, tested first, for multiples of both 3 and 5 (e.g. number MOD 15 == 0, or number MOD 3 == 0 AND number MOD 5 == 0)
(a) B1 correct condition and output for multiples of 3 only (number MOD 3 == 0)
(a) B1 correct condition and output for multiples of 5 only (number MOD 5 == 0)
(a) B1 correct final ELSE branch outputting the number itself when none of the above conditions are true

(a) Answer:

FOR number = 1 TO 30
    IF number MOD 15 == 0 THEN
        OUTPUT "FizzBuzz"
    ELSE
        IF number MOD 3 == 0 THEN
            OUTPUT "Fizz"
        ELSE
            IF number MOD 5 == 0 THEN
                OUTPUT "Buzz"
            ELSE
                OUTPUT number
            ENDIF
        ENDIF
    ENDIF
NEXT number

Question 13

(a) B1 identifies that the loop runs from index 1 to LEN(numbers), which skips index 0 (the first element) and attempts to access index LEN(numbers), which is out of range (oe; accept identification of either half of the error)
(a) Answer: The loop starts at index 1 instead of 0, so it misses the first element (index 0), and it runs up to LEN(numbers), which is one index beyond the last valid index (LEN(numbers) - 1), causing an out-of-range array access.
(b) B1 correct loop start changed to 0
(b) B1 correct loop end changed to LEN(numbers) - 1
(b) Answer: FOR i = 0 TO LEN(numbers) - 1

Question 14

(a) B1 a total variable initialised to 0 before the loops
(a) B1 correct outer loop iterating rows from 0 to 2 (oe)
(a) B1 correct inner loop iterating columns from 0 to 2, correctly nested inside the outer loop (oe)
(a) B1 correct accumulation, total = total + grid[row, column], inside the inner loop
(a) B1 OUTPUT of total placed after both loops have completed

(a) Answer:

total = 0
FOR row = 0 TO 2
    FOR column = 0 TO 2
        total = total + grid[row, column]
    NEXT column
NEXT row
OUTPUT total

Question 15

(a) B1 correct FUNCTION header with one array parameter, e.g. FUNCTION findMax(values)
(a) B1 correct initialisation of a running maximum variable, set to the first element of the array, values[0] (oe)
(a) B1 correct loop iterating through the remaining elements of the array (e.g. FOR i = 1 TO LEN(values) - 1, oe)
(a) B1 correct selection comparing each element to the running maximum and updating it whenever a larger value is found
(a) B1 correct RETURN of the maximum value after the loop has ended

(a) Answer:

FUNCTION findMax(values)
    maximum = values[0]
    FOR i = 1 TO LEN(values) - 1
        IF values[i] > maximum THEN
            maximum = values[i]
        ENDIF
    NEXT i
    RETURN maximum
ENDFUNCTION

Question 16

(a) B1 correct read file opened for reading, e.g. inFile = OPENFILE("results.txt", READ)
(a) B1 correct write file opened for writing, e.g. outFile = OPENFILE("pass.txt", WRITE)
(a) B1 a count variable initialised to 0 before the loop
(a) B1 correct condition-controlled loop reading each line WHILE NOT EOF(inFile), casting each value to an integer with INT()
(a) B1 correct selection testing mark ≥ 40 and, when true, writing the mark to outFile using WRITEFILE (with STR() to cast back to a string) and incrementing count
(a) B1 both files closed with CLOSEFILE after the loop, and count output (oe; accept close statements in either order, provided both files are closed)

(a) Answer:

inFile = OPENFILE("results.txt", READ)
outFile = OPENFILE("pass.txt", WRITE)
count = 0
WHILE NOT EOF(inFile)
    mark = INT(READFILE(inFile))
    IF mark >= 40 THEN
        WRITEFILE(outFile, STR(mark))
        count = count + 1
    ENDIF
ENDWHILE

CLOSEFILE(inFile)
CLOSEFILE(outFile)

OUTPUT count

Question 17

(a) B1 correct FUNCTION header with one string parameter, e.g. FUNCTION isValidPassword(password)
(a) B1 correct check of the length condition, LEN(password) ≥ 8 (oe)
(a) B1 a Boolean flag (e.g. containsDigit = False) initialised before searching for a digit
(a) B1 correct iteration through every character of the password (e.g. FOR i = 0 TO LEN(password) - 1, oe)
(a) B1 correct selection testing whether the current character is a digit (e.g. comparing the character against "0" to "9") and setting the flag to True when found
(a) B1 correct final RETURN combining both conditions with AND (RETURN length condition AND containsDigit, oe)

(a) Answer:

FUNCTION isValidPassword(password)
    containsDigit = False
    FOR i = 0 TO LEN(password) - 1
        character = SUBSTRING(i, 1, password)
        IF character >= "0" AND character <= "9" THEN
            containsDigit = True
        ENDIF
    NEXT i
    RETURN LEN(password) >= 8 AND containsDigit
ENDFUNCTION

Question 18

(a) B1 identifies that found is reassigned on every iteration, so its final value only reflects the last comparison made, not whether a match was found earlier in the array
(a) B1 supporting example showing a case where the target is found early but a later non-matching element overwrites found back to -1 (e.g. numbers = [4, 9, 2], target = 4: found is set to 0 at i = 0, but then overwritten to -1 at i = 1 and i = 2)
(a) Answer: The variable found is reassigned inside every loop iteration, including the ELSE branch, so a correct match found early is overwritten by later non-matches. Example: numbers = [4, 9, 2], target = 4: at i = 0, found = 0 (a correct match), but at i = 1, numbers[1] = 9 does not equal 4, so found is reset to -1, and again at i = 2. The function returns -1 even though 4 is in the array at index 0.
(b) B1 correct RETURN of i placed immediately inside the IF branch when a match is found, exiting the function immediately rather than storing it in a variable that could later be overwritten
(b) B1 removal of the incorrect ELSE branch that reset found on every non-matching element
(b) B1 correct RETURN of -1 placed after the loop, only reached if no match was found during any iteration

(b) Answer:

FUNCTION search(numbers, target)
    FOR i = 0 TO LEN(numbers) - 1
        IF numbers[i] == target THEN
            RETURN i
        ENDIF
    NEXT i
    RETURN -1
ENDFUNCTION

Question 19

(a) B1 correct file opened for reading and a condition-controlled loop that reads until WHILE NOT EOF(stockFile) becomes false
(a) B1 correct reading of a name line then a quantity line (cast to an integer with INT()) inside the loop, storing each into the respective array at index itemCount and incrementing itemCount (oe; accept declared fixed-size arrays with a running counter, or any other correct method of building the two arrays)
(a) B1 correct findItem function header taking the array, itemCount and searchName as parameters
(a) B1 correct iteration (e.g. FOR i = 0 TO itemCount - 1) and selection returning the matching index i inside the loop
(a) B1 correct RETURN of -1 placed after the loop, only reached if no match was found
(a) B1 correct INPUT for the search name, and a call to findItem storing the result in a variable
(a) B1 correct selection: IF index == -1 THEN a not-found message is output, ELSE quantities[index] is output
(a) B1 correct nested check, quantities[index] < 5, correctly nested inside the found branch, outputting a low stock warning when true

(a) Answer:

itemCount = 0
DECLARE itemNames : ARRAY[0:49] OF STRING
DECLARE quantities : ARRAY[0:49] OF INTEGER
stockFile = OPENFILE("stock.txt", READ)
WHILE NOT EOF(stockFile)
    itemNames[itemCount] = READFILE(stockFile)
    quantities[itemCount] = INT(READFILE(stockFile))
    itemCount = itemCount + 1
ENDWHILE

CLOSEFILE(stockFile)

FUNCTION findItem(itemNames, itemCount, searchName)
    FOR i = 0 TO itemCount - 1
        IF itemNames[i] == searchName THEN
            RETURN i
        ENDIF
    NEXT i
    RETURN -1
ENDFUNCTION

INPUT searchName
index = findItem(itemNames, itemCount, searchName)
IF index == -1 THEN
    OUTPUT "Item not found"
ELSE
    OUTPUT quantities[index]
    IF quantities[index] < 5 THEN
        OUTPUT "Low stock warning"
    ENDIF
ENDIF

Question 20

(a) B1 identifies that if -1 is entered first, count remains 0 after the loop
(a) B1 explains that this causes total / count to divide by zero, which is undefined/causes a runtime error, so no meaningful average can be produced
(a) Answer: If the user enters -1 as their very first input, the WHILE loop body never executes, so count stays at 0. The line average = total / count then attempts to divide by zero, which causes a runtime (division by zero) error rather than producing a sensible output.
(b) B1 correct change to the loop condition so that any negative number (not just exactly -1) ends input, e.g. WHILE number ≥ 0 (oe)
(b) B1 correct selection after the loop testing whether count == 0
(b) B1 correct output of a suitable message (e.g. "No valid numbers were entered") in the count == 0 branch
(b) B1 correct calculation and output of average retained only in the ELSE branch (when count > 0), so division by zero can no longer occur

(b) Answer:

total = 0
count = 0
INPUT number
WHILE number >= 0
    total = total + number
    count = count + 1
    INPUT number
ENDWHILE
IF count == 0 THEN
    OUTPUT "No valid numbers were entered"
ELSE
    average = total / count
    OUTPUT average
ENDIF

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