Cambridge IGCSE · 0478

Computer Science

Algorithms, programming and logic — Paper 2

Name: ____________________Date: October 14, 2026

1.
Write pseudocode that repeatedly inputs a test score until the value is between 0 and 100 inclusive, then outputs ‘valid’. Use a post-test or pre-test loop.
[4 marks] · no calculator
Marking points
- Inputs a score before or within a suitable loop.
- Tests both lower and upper bounds correctly.
- Repeats while the score is outside 0 to 100, with correct Boolean logic.
- Outputs the valid message only after the loop terminates.
Examiner tip: For an invalid value use score < 0 OR score > 100; using AND makes the condition impossible.
2.
A program calculates delivery charges from parcel weight. Design four test cases covering normal, boundary, invalid and extreme data. State the input and purpose of each case.
[4 marks] · no calculator
Marking points
- Provides a plausible normal value and labels its purpose.
- Provides an exact boundary value relevant to a charging band.
- Provides invalid data such as a negative weight or wrong data type.
- Provides an extreme but valid value and explains the stress being tested.
Examiner tip: A boundary test uses the exact limit; values just below and above it are additional boundary checks.
3.
Write pseudocode to find and output the largest value in an array of 10 integers called Scores.
[4 marks] · no calculator
Marking points
- Declares a variable to hold the largest value, initialised to the first array element.
- Uses a loop to traverse the remaining elements of the array.
- Compares each element to the current largest value and updates it when a bigger value is found.
- Outputs the largest value after the loop ends.
Examiner tip: Initialise the 'largest' variable with the first element, not zero — scores could be negative or the array could contain only small positive values.
4.
The list [5, 2, 8, 1] is sorted into ascending order using a bubble sort. State the list after the first full pass.
[3 marks] · no calculator
Marking points
- Compares 5 and 2, swaps them to give [2, 5, 8, 1].
- Compares 5 and 8, no swap needed, giving [2, 5, 8, 1].
- Compares 8 and 1, swaps them to give the final first-pass result [2, 5, 1, 8].
Examiner tip: A bubble sort compares each adjacent pair in turn during a pass, swapping whenever the left value is greater than the right.
5.
A list of 1,000 names is already sorted alphabetically. Which search algorithm will generally find a specific name fastest? A Linear search B Binary search C Bubble sort D Insertion sort
[1 mark] · no calculator
Marking points
- Selects B: binary search repeatedly halves a sorted list, finding items far faster than checking each one in turn.
Examiner tip: Binary search requires the list to already be sorted; it cannot be used correctly on unsorted data.
6.
Write pseudocode using nested IF statements that outputs a grade for a given Score: 'A' if the score is 90 or above, 'B' if it is 75 or above but below 90, and 'C' otherwise.
[3 marks] · no calculator
Marking points
- Tests the highest condition first: IF Score >= 90 THEN output 'A'.
- Nests an ELSE IF (or ELSE containing IF) testing Score >= 75 to output 'B'.
- Provides a final ELSE branch that outputs 'C' for any remaining score.
Examiner tip: Testing from the highest boundary downward avoids a lower condition like Score >= 75 wrongly catching a 95 before it reaches the 'A' check.
7.
Explain one advantage of using a function (subroutine) rather than repeating the same code several times in a program.
[2 marks] · no calculator
Marking points
- Explains that a function keeps the logic in one place, so the program is shorter and easier to read.
- Explains that if the logic needs to change, it only needs to be updated once inside the function, reducing errors and maintenance effort.
Examiner tip: Repeated code must be found and changed everywhere it appears; a function only needs to be changed once.
8.
A form asks a user to enter their age as a whole number between 1 and 120. Identify two different validation checks that could be applied, and explain what each one checks for.
[4 marks] · no calculator
Marking points
- Identifies a range check.
- Explains that a range check confirms the value falls between 1 and 120 inclusive.
- Identifies a type check.
- Explains that a type check confirms the value entered is a whole number (integer), not text or a decimal.
Examiner tip: A range check and a type check examine different properties of the same input and are often both needed together.
9.
A loop runs the pseudocode 'Count ← Count + 1' three times, starting with Count = 0. Complete a trace table showing the value of Count after each of the three iterations.
[3 marks] · no calculator
Marking points
- States that Count = 1 after the first iteration.
- States that Count = 2 after the second iteration.
- States that Count = 3 after the third iteration.
Examiner tip: A trace table tracks how a variable's value changes step by step as a program or loop executes.
10.
Write pseudocode to calculate and output the average of 5 numbers stored in an array called Marks.
[4 marks] · no calculator
Marking points
- Declares a total variable initialised to zero before the loop.
- Uses a loop to add each of the 5 array elements to the total.
- Divides the final total by 5 after the loop ends to calculate the average.
- Outputs the calculated average.
Examiner tip: Always initialise a running total to zero before a loop begins adding to it; forgetting this gives an incorrect result.
11.
Explain the difference between a variable and a constant in a program.
[2 marks] · no calculator
Marking points
- Explains that a variable's value can be changed while the program is running.
- Explains that a constant's value is fixed and set once, and cannot be changed while the program runs.
Examiner tip: Use a constant for a value that should never change during execution, such as the number of days in a week, to prevent it being accidentally altered.
12.
Explain why a 2D array would be a suitable data structure to store the seating plan of a cinema with rows and columns of seats.
[2 marks] · no calculator
Marking points
- Explains that a 2D array organises data using two indices, which can directly represent a row number and a column number.
- Explains that this makes it easy to store and access the status of a seat at any specific row and column position, matching the real layout.
Examiner tip: A 2D array is a natural fit whenever real-world data is already organised in a grid, such as rows and columns of seats.
13.
Explain what the string length function would return when applied to the text 'Cambridge', and give one reason a programmer might need this value.
[2 marks] · no calculator
Marking points
- States that the length function would return 9, since 'Cambridge' has 9 characters.
- States a valid reason, such as validating that a username or password meets a minimum or maximum length requirement.
Examiner tip: String length functions are commonly used in validation, to check an input is neither too short nor too long before accepting it.
14.
Distinguish between a count-controlled loop and a condition-controlled loop, using an example of when each would be appropriate.
[2 marks] · no calculator
Marking points
- Explains that a count-controlled loop (such as a FOR loop) repeats a fixed, known number of times, suitable for processing every element of an array of known size.
- Explains that a condition-controlled loop (such as a WHILE loop) repeats until a condition becomes true or false, suitable when the number of repetitions is not known in advance, such as repeating until valid input is entered.
Examiner tip: Choose a count-controlled loop when you know exactly how many repetitions you need in advance; choose a condition-controlled loop when you do not.
15.
The list [8, 3, 6, 1] is sorted into ascending order using an insertion sort. State the list after the algorithm has correctly inserted the second element (3) into its sorted position among the first two elements.
[2 marks] · no calculator
Marking points
- Compares 3 with 8 and finds 3 is smaller.
- Shifts 8 to the right and inserts 3 before it, giving [3, 8, 6, 1].
Examiner tip: Insertion sort builds a sorted section at the start of the list one element at a time, shifting larger elements right to make room.
16.
Write pseudocode for a linear search that looks for a Target value in an array called Items, and outputs whether the value was found.
[4 marks] · no calculator
Marking points
- Uses a loop to check each element of the array in turn, starting from the first.
- Compares each element to the Target value.
- Outputs that the value was found if a match is found during the loop.
- Outputs that the value was not found if the loop completes without finding a match.
Examiner tip: A linear search checks every element one at a time until a match is found or the list ends — simple, but slower than binary search on large sorted lists.
17.
Explain what a decision (diamond-shaped) symbol represents in a flowchart.
[2 marks] · no calculator
Marking points
- Explains that a decision symbol represents a point where the program checks a condition, which is either true or false.
- Explains that the flowchart branches into different paths depending on the result of this check.
Examiner tip: Every path leaving a decision symbol should be clearly labelled, usually 'Yes'/'No' or 'True'/'False'.
18.
Write pseudocode to count how many values in an array called Scores are greater than 50.
[4 marks] · no calculator
Marking points
- Declares a counter variable initialised to zero before the loop.
- Uses a loop to check every element of the array in turn.
- Increases the counter by 1 only when an element is greater than 50.
- Outputs the final counter value after the loop ends.
Examiner tip: A counting algorithm only increases its counter when the condition is met, unlike a totaling algorithm, which adds the actual value every time.
19.
Explain one advantage of writing a procedure that accepts parameters, rather than one that always works on fixed, built-in values.
[2 marks] · no calculator
Marking points
- Explains that a procedure with parameters can be reused with different input values each time it is called, instead of only ever working on one fixed value.
- Explains that this makes the code more flexible and avoids having to write a near-identical procedure for every different input value needed.
Examiner tip: Parameters let one procedure handle many different cases, rather than needing a separate, duplicated procedure for each specific value.
20.
A form requires a user to enter their name. Explain what a presence check would do, and why it is needed for this field.
[2 marks] · no calculator
Marking points
- Explains that a presence check confirms that the user has not left the field completely empty.
- Explains that this is needed because a name field is a required piece of data, and the program should not accept a submission that is missing it.
Examiner tip: A presence check is the simplest form of validation: it only confirms that something was entered, not that it is the right kind of data.
21.
A system requires a new password to be at least 8 characters long. Explain what a length check would do when this password is entered.
[2 marks] · no calculator
Marking points
- Explains that a length check counts the number of characters entered.
- Explains that it rejects the input if this count is below the minimum (or above a maximum, if one is set) allowed length.
Examiner tip: A length check specifically counts characters; it does not check whether those characters are of the correct type.
22.
Explain, in simple terms, what it means for a function to be recursive, using a function that calculates factorials as an example.
[2 marks] · no calculator
Marking points
- Explains that a recursive function is a function that calls itself as part of its own execution.
- Applies this to the example: a factorial function can calculate factorial(n) by calling itself to calculate factorial(n-1), and so on, until it reaches a base case.
Examiner tip: Every recursive function needs a base case — a point where it stops calling itself — otherwise it would repeat forever.
23.
Explain one feature of an Integrated Development Environment (IDE) that helps a programmer write code with fewer errors.
[2 marks] · no calculator
Marking points
- Identifies a valid feature, such as syntax highlighting, auto-complete, or a built-in debugger.
- Explains how this feature helps, such as syntax highlighting making it easier to spot a missing bracket or misspelled keyword.
Examiner tip: IDE tools exist specifically to catch common mistakes early, before the program is even run.
24.
Explain the purpose of using meaningful variable names, such as 'studentAge' instead of 'x', when writing a program.
[2 marks] · no calculator
Marking points
- Explains that a meaningful name makes it clear what kind of data the variable stores, without needing to read the surrounding code carefully.
- Explains that this makes the program easier for the original programmer, or someone else, to read, understand and maintain later.
Examiner tip: Meaningful names cost nothing to the computer running the program, but save real time for any human who later reads the code.