Explaining The Purpose Of An Algorithm

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What the Syllabus Requires

Section 7.3 requires you to explain the purpose of a given algorithm, which includes stating the purpose and describing the processes involved.
Algorithms may be given as pseudocode, flowcharts, or structure diagrams.
Section 7.2 frames problems in terms of inputs, processes, outputs, and storage – use this vocabulary in answers.
Standard methods you must recognise: linear search, bubble sort, totalling, counting, finding maximum/minimum/average, validation, and authentication.
Unseen algorithms on Paper 2 are usually one of these methods or a short combination.

The Two Commands

"State the purpose" (1–2 marks): give one sentence naming the overall job and the data it works on.
Do not narrate the code line-by-line; that scores nothing.
"Describe the processes" (3–4 marks): give the ordered steps in technical language – inputs, storage, repetition, decisions, outputs.
Usually one mark per identified process, so write one clear point per mark.
Match answer length to marks: one sentence for 1 mark, one point per mark for describe.

Five-Step Method to Find the Purpose

1. Read the OUTPUT statements first – what is finally output is usually what the algorithm is for.
2. Find initialisations – `Total ← 0` signals totalling, `Count ← 0` signals counting, `Max ← first value` signals finding a maximum, `Found ← FALSE` signals a search.
3. Look at the loop – a `FOR` loop over an array means 'every item'; a `WHILE` with a `Found` flag means 'stop early when match'; a `REPEAT...UNTIL` around `INPUT` means validation.
4. Look at the condition inside the loop – `IF Value > Max` means finding largest; `IF Value < 40` with counter means counting a category; comparing and swapping neighbours means bubble sort.
5. Say it in one sentence using real quantities: what data it takes in, what it does, what it gives back – with actual range, size, or threshold.

Sentence Templates That Earn Marks

Totalling/Average: "It inputs <n> <values> and outputs the total / average of them."
Counting: "It counts how many of the <n> <values> are <condition> and outputs that count."
Maximum/Minimum: "It finds and outputs the largest / smallest value in the array <Name> and, where relevant, its position."
Search: "It searches the array <Name> for <SearchItem> and outputs its position, or a message if it is not there."
Sort: "It sorts the array <Name> into ascending / descending order."
Validation: "It validates the input <Name>, rejecting values outside <range> and re-prompting until an acceptable value is entered."
Authentication: "It checks a password against a stored value and allows a maximum of <n> attempts."

Worked Example 1 – Totalling and Counting

Pseudocode: initialises `Count` and `Total` to 0, loops 30 times, inputs a `Mark`, adds to `Total`, increments `Count` if `Mark < 40`, then outputs average and count.
Purpose: "It inputs 30 marks, then outputs their average and how many of them were below 40."
Processes: total and counter initialised; count-controlled loop inputs each mark; each mark added to total; if less than 40, counter incremented; after loop, total divided by 30 to give average; average and count output.
Not acceptable: "it works out marks", "it uses a loop 30 times", "it checks if the mark is less than 40".

Worked Example 2 – Finding Maximum

Pseudocode: sets `Max` to first temperature, `Position` to 1, loops from index 2 to 7, updates `Max` and `Position` if current temperature is greater, then outputs highest and day.
Purpose: "It finds the highest of the seven stored temperatures and outputs it together with the day it occurred."
Note precision: array holds seven values, and algorithm reports position as well as value.
Starting `Max` at the first element (not 0) makes it work for negative temperatures – a good point when describing processes.

Worked Example 3 – Validation

Pseudocode: `REPEAT` output prompt, input `Age`, `UNTIL Age ≥ 11 AND Age ≤ 18`, then output "Thank you".
Purpose: "It validates the age entered by the user, repeatedly re-prompting until a value between 11 and 18 inclusive is entered."
Technical term: a range check performed by a post-condition loop.
Saying "it makes sure the age is right" does not score.

Worked Example 4 – Flowchart

A flowchart with start terminator, input, decision diamond, and two output branches.
Purpose: "It inputs a temperature and outputs a warning if it is above 30°, otherwise it outputs that conditions are normal."
Use standard symbols as reading guide: terminator (start/stop), input/output parallelogram, process rectangle, decision diamond, subroutine, and flow-line arrows showing order.

Precision Rules for Wording

Name the data as the algorithm names it: the array `Temperature`, the variable `Count`, the 30 marks.
Give the actual threshold, range, or size: "below 40", "between 11 and 18 inclusive", "the seven values".
Use verbs that name the method: inputs, validates, totals, counts, searches, sorts into ascending order, compares, swaps, outputs. Avoid: does, gets, deals with, checks stuff, sorts it out.
Say ascending or descending – never just "sorts".
Do not describe syntax (e.g., "it uses a FOR loop") unless asked for processes; even then, say what the loop achieves.
Do not invent behaviour not in the code, and do not state the purpose of only part of it – if it both totals and counts, include both halves.

Why This Skill Pays Off Elsewhere

Recognising the purpose quickly makes the rest of Paper 2 faster.
It tells you what a trace table should end up showing (section 7.7).
It helps identify errors and suggest corrections (section 7.8).
It gives you the plan sentence for the final 15-mark scenario question (about 30 minutes).

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1.What is the purpose of an algorithm?
Easy
- ATo provide a step-by-step set of instructions to solve a problem
- BTo store data in a database
- CTo create a graphical user interface
- DTo compile a program
2.When asked to 'state the purpose of an algorithm', what should your answer include?
Easy
- AA line-by-line explanation of the code
- BA single sentence describing the overall job of the algorithm
- CA list of all variables used
- DA description of the syntax of the programming language
3.When describing the processes involved in an algorithm, you should write one clear point per mark available.
Easy
True or false?
4.Which of the following is an example of a standard method that an algorithm might use?
Easy
- ALinear search
- BObject-oriented programming
- CRecursion
- DMachine learning
5.Which of the following are standard methods that you should be able to recognise in an algorithm? (Select all that apply)
Easy
- ALinear search
- BBubble sort
- CTotalling
- DCounting
- ERecursion
6.In an algorithm, the statement 'Total ← 0' before a loop typically indicates that the algorithm is totalling values.
Easy
True or false?
7.An algorithm contains the following pseudocode: Max ← Temperature[1] FOR Index ← 2 TO 7 IF Temperature[Index] > Max THEN Max ← Temperature[Index] ENDIF NEXT Index What is the purpose of this algorithm?
Medium
- AIt finds the highest temperature in the array Temperature and outputs it.
- BIt sorts the array Temperature into ascending order.
- CIt counts the number of temperatures above a threshold.
- DIt calculates the average temperature.
8.Which of the following statements is NOT an acceptable purpose for an algorithm?
Medium
- AIt inputs 30 marks, then outputs their average and how many of them were below 40.
- BIt sets Count to 0, then loops through the array.
- CIt finds the highest of the seven stored temperatures and outputs it together with the day it occurred.
- DIt validates the age entered by the user, repeatedly re-prompting until a value between 11 and 18 inclusive is entered.

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9.An algorithm is given as a flowchart. What is the purpose of the algorithm described by the flowchart?
Medium
- AIt inputs a temperature and outputs a warning if it is above 30°, otherwise it outputs that conditions are normal.
- BIt inputs a temperature and outputs the average of all temperatures.
- CIt sorts the temperatures into ascending order.
- DIt counts the number of temperatures above 30°.
10.Match the initialisation to the standard method it indicates.
Medium
- Total ← 0
- Count ← 0
- Max ← first value
- Totalling
- Counting
- Finding maximum
11.Put the following steps in the correct order for reading an algorithm to work out its purpose.
Medium
- Read the OUTPUT statements first.
- Find the initialisations before the loop.
- Look at the loop.
- Look at the condition inside the loop.
- Say it in one sentence using the real quantities.
12.What does the following algorithm do? Count ← 0 Total ← 0 FOR Index ← 1 TO 30 INPUT Mark Total ← Total + Mark IF Mark < 40 THEN Count ← Count + 1 ENDIF NEXT Index OUTPUT "Average is ", Total / 30 OUTPUT Count, " marks were below 40"
Medium
- AIt inputs 30 marks, then outputs their average and how many of them were below 40.
- BIt inputs 30 marks and outputs the total and the number of marks above 40.
- CIt inputs 30 marks and outputs the highest mark and the number of marks below 40.
- DIt inputs 30 marks and sorts them into ascending order.
13.In the algorithm below, what is the purpose of the variable 'Position'? Max ← Temperature[1] Position ← 1 FOR Index ← 2 TO 7 IF Temperature[Index] > Max THEN Max ← Temperature[Index] Position ← Index ENDIF NEXT Index OUTPUT "Highest was ", Max, " on day ", Position
Medium
- ATo store the index of the highest temperature
- BTo store the highest temperature value
- CTo count the number of temperatures
- DTo store the average temperature
14.In the algorithm below, the variable 'Max' is initialised to 0, which is correct for finding the maximum even if all temperatures are negative. Max ← 0 FOR Index ← 1 TO 7 IF Temperature[Index] > Max THEN Max ← Temperature[Index] ENDIF NEXT Index OUTPUT Max
Medium
True or false?
15.An algorithm contains the following pseudocode: FOR Index ← 1 TO 4 FOR J ← 1 TO 4 - Index IF Array[J] > Array[J+1] THEN Temp ← Array[J] Array[J] ← Array[J+1] Array[J+1] ← Temp ENDIF NEXT J NEXT Index What is the purpose of this algorithm?
Hard
- AIt sorts the array into ascending order.
- BIt sorts the array into descending order.
- CIt searches for a value in the array.
- DIt finds the maximum value in the array.
16.An algorithm contains the following pseudocode: Found ← FALSE Index ← 1 WHILE Found = FALSE AND Index ≤ 100 IF Names[Index] = SearchName THEN Found ← TRUE ELSE Index ← Index + 1 ENDIF ENDWHILE IF Found = TRUE THEN OUTPUT "Found at position ", Index ELSE OUTPUT "Not found" ENDIF What is the purpose of this algorithm?
Hard
- AIt searches the array Names for SearchName and outputs its position or a message if it is not there.
- BIt sorts the array Names into ascending order.
- CIt counts how many times SearchName appears in the array.
- DIt finds the maximum value in the array.
17.An algorithm is given as a structure diagram. Which of the following best describes the purpose of the algorithm?
Challenge
- AIt inputs a list of numbers, totals them, and outputs the average.
- BIt inputs a list of numbers and sorts them into descending order.
- CIt inputs a list of numbers and finds the minimum value.
- DIt inputs a list of numbers and counts the number of positive values.
18.Match each algorithm component to its typical purpose.
Challenge
- REPEAT...UNTIL around an INPUT
- WHILE with a Found flag
- FOR loop over an array
- Validation of user input
- Search that stops early
- Process every item
19.When describing the processes involved in an algorithm, it is acceptable to say 'it uses a FOR loop' as a complete answer.
Challenge
True or false?
20.Match each initialisation to the standard method it indicates.
Easy
- Total ← 0
- Count ← 0
- Found ← FALSE
- totalling values
- counting values
- searching for an item
21.Put the steps in the correct order for reading an algorithm to work out its purpose.
Medium
- Read the OUTPUT statements first.
- Find the initialisations before the loop.
- Look at the loop structure.
- Look at the condition inside the loop.
- State the purpose in one sentence.
22.Which of the following are acceptable ways to describe the purpose of an algorithm? (Select all that apply)
Medium
- AIt inputs 30 marks and outputs their average.
- BIt uses a FOR loop 30 times.
- CIt counts how many of the 30 marks are below 40.
- DIt checks if each mark is less than 40.
- EIt sorts the array into ascending order.
23.When asked to 'state the purpose of an algorithm', you should describe the steps the algorithm performs in order.
Easy
True or false?
24.Study the algorithm below. Max ← Temperature[1] Position ← 1 FOR Index ← 2 TO 7 IF Temperature[Index] > Max THEN Max ← Temperature[Index] Position ← Index ENDIF NEXT Index OUTPUT "Highest was ", Max, " on day ", Position What is the purpose of this algorithm?
Medium
- AIt finds the highest of the seven stored temperatures and outputs it together with the day it occurred.
- BIt sorts the seven temperatures into ascending order and outputs the highest.
- CIt counts how many temperatures are above the first temperature.
- DIt outputs the average temperature of the seven days.
25.When describing the processes involved in an algorithm, saying 'it uses a FOR loop' is a complete answer.
Easy
True or false?
26.An algorithm is described by the following pseudocode: Total ← 0 FOR Index ← 1 TO 10 INPUT Value Total ← Total + Value NEXT Index OUTPUT Total / 10 What is the purpose of this algorithm?
Easy
- AIt inputs 10 values and outputs their total.
- BIt inputs 10 values and outputs their average.
- CIt inputs 10 values and counts how many are above average.
- DIt inputs 10 values and finds the largest value.
27.Study the following algorithm: Max ← 0 FOR Index ← 1 TO 5 INPUT Number IF Number > Max THEN Max ← Number ENDIF NEXT Index OUTPUT Max What is the purpose of this algorithm?
Medium
- AIt finds the largest of the five input numbers.
- BIt finds the smallest of the five input numbers.
- CIt counts how many numbers are greater than 0.
- DIt sums the five input numbers.
28.The algorithm uses a REPEAT...UNTIL loop to check the password.
Easy
True or false?
29.The following algorithm is intended to sort an array of numbers into ascending order. Which standard method does it use? FOR Index ← 1 TO 4 FOR J ← 1 TO 4 - Index IF Array[J] > Array[J+1] THEN Temp ← Array[J] Array[J] ← Array[J+1] Array[J+1] ← Temp ENDIF NEXT J NEXT Index
Hard
- ALinear search
- BBubble sort
- CSelection sort
- DInsertion sort
30.A student is writing an algorithm to find the average of 10 numbers. Which initialisation is correct?
Medium
- ATotal ← 0 and Count ← 0
- BTotal ← 1 and Count ← 1
- CTotal ← 0 and Count ← 1
- DTotal ← 1 and Count ← 0
31.An algorithm contains the following pseudocode: Max ← List[1] FOR Index ← 2 TO 10 IF List[Index] > Max THEN Max ← List[Index] ENDIF NEXT Index OUTPUT Max What is the purpose of this algorithm?
Medium
- AIt finds the largest value in the list and outputs it.
- BIt finds the smallest value in the list and outputs it.
- CIt sorts the list into ascending order.
- DIt outputs the sum of all values in the list.
32.An algorithm is designed to validate a user's age. Which of the following pseudocode snippets correctly validates that the age is between 11 and 18 inclusive, repeating until a valid value is entered?
Medium
- AREPEAT INPUT Age UNTIL Age ≥ 11 AND Age ≤ 18
- BREPEAT INPUT Age UNTIL Age ≥ 11 OR Age ≤ 18
- CWHILE Age < 11 OR Age > 18 INPUT Age ENDWHILE
- DFOR Index ← 1 TO 10 INPUT Age NEXT Index
33.What is the purpose of the algorithm?
Medium
- AIt inputs a temperature and outputs a warning if it is above 30°, otherwise it outputs that conditions are normal.
- BIt inputs a temperature and outputs the temperature value.
- CIt checks if the temperature is exactly 30° and outputs a message.
- DIt sorts temperatures into ascending order.
34.In the context of explaining an algorithm, what does 'stating the purpose' mean?
Easy
- ADescribing the overall job of the algorithm in one sentence
- BListing each line of the algorithm in order
- CIdentifying the programming language used
- DExplaining the syntax of the pseudocode
35.Which of the following is the best description of the purpose of an algorithm?
Easy
- AIt finds the largest value in an array
- BIt sets a variable to 0 and then loops through an array
- CIt uses a FOR loop
- DIt stores values in an array
36.Which of the following is NOT an acceptable way to describe the purpose of an algorithm?
Easy
- AIt checks if a number is positive
- BIt uses a FOR loop to iterate through an array
- CIt outputs the average of 10 numbers
- DIt counts how many values are above 50
37.Match each algorithm component to its typical purpose in understanding an algorithm.
Medium
- OUTPUT statement
- Initialisation Total ← 0
- WHILE with Found flag
- REPEAT...UNTIL around INPUT
- Indicates the algorithm's overall job
- Indicates totalling
- Indicates a search
- Indicates validation of user input
38.Put the steps in the correct order to work out the purpose of an algorithm.
Medium
- Read the OUTPUT statements first
- Find the initialisations before the loop
- Look at the loop structure
- Look at the condition inside the loop
- Say the purpose in one sentence using real quantities
39.When asked to 'describe the processes involved in an algorithm', it is acceptable to say 'it uses a FOR loop' as a complete answer.
Easy
True or false?
40.An algorithm is designed to find the minimum value in an array of 50 test scores. The variable Min is initialised to List[1]. Why is it important to initialise Min to List[1] rather than to 0?
Medium
- ABecause all test scores are positive, so 0 would work, but List[1] is more efficient.
- BBecause if all scores are negative, starting at 0 would incorrectly output 0 as the minimum.
- CBecause it ensures the loop runs exactly 50 times.
- DBecause it makes the algorithm easier to read.
41.Complete the sentence with the correct term.
Easy
The process of breaking a problem down into smaller sub-problems is called ____.
42.In the algorithm below, how many times is the loop executed? FOR Index ← 1 TO 5 OUTPUT Index NEXT Index
Hard
43.What standard method is indicated by 'Max ← Temperature[1]'?
Easy
44.An algorithm contains the following loop. How many times is the loop executed? FOR Index ← 1 TO 30 INPUT Mark NEXT Index
Easy
45.The following algorithm is intended to find the maximum value in a list of 10 numbers. How many times is the loop executed? Max ← List[1] FOR Index ← 2 TO 10 IF List[Index] > Max THEN Max ← List[Index] ENDIF NEXT Index
Medium
46.In the algorithm below, what is the value of Total output after the loop completes? Total ← 0 FOR Index ← 1 TO 4 INPUT Value Total ← Total + Value NEXT Index OUTPUT Total
Easy
47.Complete the sentence: When asked to 'state the purpose of an algorithm', you should give a ___ sentence that describes the overall job, not a line-by-line narration.
Easy
When asked to 'state the purpose of an algorithm', you should give a ____ sentence that describes the overall job, not a line-by-line narration.
48.Complete the sentence: In the algorithm below, the variable Total is initialised to 0 before the loop, which indicates that the algorithm is ___ the input values. Total ← 0 FOR Index ← 1 TO 10 INPUT Value Total ← Total + Value NEXT Index OUTPUT Total
Medium
In the algorithm below, the variable Total is initialised to 0 before the loop, which indicates that the algorithm is ____ the input values.
49.Complete the sentence: To find the maximum value in an array, the variable Max should be initialised to the ___ element of the array, rather than to 0, so that the algorithm works correctly even if all values are negative.
Easy
To find the maximum value in an array, the variable Max should be initialised to the ____ element of the array, rather than to 0, so that the algorithm works correctly even if all values are negative.
50.What is the technical term for the standard method used in the algorithm below? Found ← FALSE Index ← 1 WHILE Found = FALSE AND Index ≤ 100 IF Names[Index] = SearchName THEN Found ← TRUE ELSE Index ← Index + 1 ENDIF ENDWHILE IF Found = TRUE THEN OUTPUT Index ELSE OUTPUT "Not found"
Easy
51.What is the technical term for the standard method used in the algorithm below? FOR Index ← 1 TO 4 FOR J ← 1 TO 4 - Index IF Array[J] > Array[J+1] THEN Temp ← Array[J] Array[J] ← Array[J+1] Array[J+1] ← Temp ENDIF NEXT J NEXT Index
Easy
52.In the algorithm below, how many times is the loop executed? FOR Index ← 2 TO 10 OUTPUT Index NEXT Index
Medium
53.What is the purpose of an algorithm that uses a REPEAT...UNTIL loop to repeatedly ask for input until a value between 11 and 18 inclusive is entered?
Medium
54.Describe the processes involved in the algorithm shown below. Count ← 0 Total ← 0 FOR Index ← 1 TO 30 INPUT Mark Total ← Total + Mark IF Mark < 40 THEN Count ← Count + 1 ENDIF NEXT Index OUTPUT "Average is ", Total / 30 OUTPUT Count, " marks were below 40"
Medium
55.State the purpose of the algorithm shown below. REPEAT OUTPUT "Enter your age" INPUT Age UNTIL Age ≥ 11 AND Age ≤ 18 OUTPUT "Thank you"
Medium
56.What is the purpose of an algorithm that checks a password against a stored value and allows a maximum of 3 attempts?
Medium
57.Explain why it is important to start the variable Max at the first element of an array rather than at 0 when finding the maximum value.
Hard
58.In the algorithm below, how many times is the loop executed? FOR Index ← 1 TO 5 OUTPUT Index NEXT Index
Hard
- A7
- B4
- C5
- D6
59.An algorithm contains the following loop. How many times is the loop executed? FOR Index ← 1 TO 30 INPUT Mark NEXT Index
Easy
- A30
- B36
- C33
- D27
60.The following algorithm is intended to find the maximum value in a list of 10 numbers. How many times is the loop executed? Max ← List[1] FOR Index ← 2 TO 10 IF List[Index] > Max THEN Max ← List[Index] ENDIF NEXT Index
Medium
- A9
- B11
- C8
- D10
61.In the algorithm below, what is the value of Total output after the loop completes? Total ← 0 FOR Index ← 1 TO 4 INPUT Value Total ← Total + Value NEXT Index OUTPUT Total
Easy
- A12
- B11
- C9
- D10
62.In the algorithm below, how many times is the loop executed? FOR Index ← 2 TO 10 OUTPUT Index NEXT Index
Medium
- A8
- B11
- C10
- D9

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## Explaining the Purpose of an Algorithm (CIE 0478) ### The Two Commands - **State the purpose** (1–2 marks): one sentence naming the overall job and the data it works on. Do **not** narrate the code line-by-line. - **Describe the processes** (3–4 marks): ordered steps in technical language – inputs, storage, repetition, decisions, outputs. One point per mark. ### How to Find the Purpose (5 Steps) 1. **Read the OUTPUT statements first** – they usually reveal the purpose. 2. **Find initialisations** – `Total ← 0` (totalling), `Count ← 0` (counting), `Max ← first value` (finding max), `Found ← FALSE` (search). 3. **Look at the loop** – `FOR` over an array = every item; `WHILE` with a flag = stop early on match; `REPEAT...UNTIL` around input = validation. 4. **Look at the condition** – `IF Value > Max` (largest), `IF Value < 40` with counter (counting category), comparing neighbours and swapping = bubble sort. 5. **Say it in one sentence** using real quantities: what data, what it does, what it outputs – include actual range/size/threshold. ### Sentence Templates - "It inputs <n> <values> and outputs the total / average of them." - "It counts how many of the <n> <values> are <condition> and outputs that count." - "It finds and outputs the largest / smallest value in the array <Name> and, where relevant, its position." - "It searches the array <Name> for <SearchItem> and outputs its position, or a message if it is not there." - "It sorts the array <Name> into ascending / descending order." - "It validates the input <Name>, rejecting values outside <range> and re-prompting until an acceptable value is entered." - "It checks a password against a stored value and allows a maximum of <n> attempts." ### Worked Examples **Example 1 (totalling + counting)** ``` Count ← 0 Total ← 0 FOR Index ← 1 TO 30 INPUT Mark Total ← Total + Mark IF Mark < 40 THEN Count ← Count + 1 ENDIF NEXT Index OUTPUT "Average is ", Total / 30 OUTPUT Count, " marks were below 40" ``` - **Purpose**: It inputs 30 marks, then outputs their average and how many were below 40. - **Processes**: Initialise total and counter to zero; loop 30 times inputting each mark; add to total; if mark < 40, increment counter; after loop, divide total by 30 and output average and count. **Example 2 (finding max)** ``` Max ← Temperature[1] Position ← 1 FOR Index ← 2 TO 7 IF Temperature[Index] > Max THEN Max ← Temperature[Index] Position ← Index ENDIF NEXT Index OUTPUT "Highest was ", Max, " on day ", Position ``` - **Purpose**: It finds the highest of the seven stored temperatures and outputs it together with the day it occurred. - **Processes**: Initialise Max and Position to first element; loop from 2 to 7; compare each element; update Max and Position if larger; output Max and Position. Starting Max at first element works for negative temperatures. **Example 3 (validation)** ``` REPEAT OUTPUT "Enter your age" INPUT Age UNTIL Age >= 11 AND Age <= 18 OUTPUT "Thank you" ``` - **Purpose**: It validates the age entered by the user, repeatedly re-prompting until a value between 11 and 18 inclusive is entered. - **Processes**: Output prompt; input age; check if age is in range; if not, repeat; when valid, output thank you. This is a range check using a post-condition loop. ### Precision Rules - Name data as the algorithm does (e.g., `Temperature`, `Count`). - Give actual thresholds/ranges/sizes (e.g., "below 40", "between 11 and 18 inclusive"). - Use method verbs: inputs, validates, totals, counts, searches, sorts into ascending order, compares, swaps, outputs. Avoid vague words like "does", "gets", "checks stuff". - Say **ascending** or **descending** – never just "sorts". - Don't describe syntax unless asked for processes; if you do, also say what the loop achieves. - Don't invent behaviour not in the code; cover all parts (e.g., both total and count). - Match answer length to marks: one sentence for 1-mark state, one point per mark for describe. ### Why It Matters Recognising purpose fast helps with trace tables (7.7), error identification (7.8), and the final 15-mark scenario question (spend ~30 minutes).

Algorithm: A step-by-step set of rules or instructions to solve a problem.
Purpose of an algorithm: A one-sentence statement of the overall job the algorithm does, including the data it works on and what it outputs.
Processes involved: The ordered steps an algorithm performs, described in technical language: inputs, storage, repetition, decisions, and outputs.
Inputs: Data that is entered into an algorithm, often via INPUT statements or from an array.
Processes: The operations performed on data, such as calculations, comparisons, and assignments.
Outputs: The results produced by an algorithm, usually via OUTPUT statements.
Storage: Variables and arrays used to hold data during the execution of an algorithm.
Linear search: A method that checks each item in a list in order until the desired item is found or the end is reached.
Bubble sort: A sorting method that repeatedly compares adjacent elements and swaps them if they are in the wrong order, until the list is sorted.
Totalling: Adding up a set of values, often using a running total variable initialised to zero.
Counting: Incrementing a counter variable each time a condition is met, to count occurrences.
Finding maximum/minimum: Scanning a list to find the largest or smallest value, often by comparing each element with a current maximum/minimum.
Average: The sum of values divided by the number of values.
Validation: Checking that input data meets certain criteria, and re-prompting until acceptable data is entered.
Authentication: Verifying a user's identity, often by checking a password against a stored value.
Range check: A validation check that ensures a value falls within a specified range (e.g., between 11 and 18 inclusive).
Trace table: A table used to manually track the values of variables and outputs as an algorithm is executed step by step.

Thẻ ghi nhớ

What is the purpose of an algorithm?

The purpose is the overall job it does, stated in one precise sentence, not a line-by-line narration of the code.

What are the two commands used in Paper 2 for explaining algorithms?

'State the purpose' (1-2 marks) asks for the overall job; 'Describe the processes involved' (3-4 marks) asks for the ordered steps in technical language.

What is the first step in reading an algorithm to determine its purpose?

Read the OUTPUT statements first, as they usually indicate what the algorithm is for.

What does 'Total ← 0' before a loop indicate?

It indicates that the algorithm is totalling (summing) values.

What does 'Count ← 0' before a loop indicate?

It indicates that the algorithm is counting occurrences of something.

What does 'Max ← first value' or 'Max ← very low value' indicate?

It indicates finding the maximum value in a set of data.

What does 'Found ← FALSE' before a loop indicate?

It indicates a search algorithm that stops early when a match is found.

What does a FOR loop over an array indicate?

It means the algorithm processes every item in the array.

What does a WHILE loop with a Found flag indicate?

It indicates a search that stops early when the item is found.

What does a REPEAT...UNTIL loop around an INPUT indicate?

It indicates validation of user input, re-prompting until an acceptable value is entered.

What does 'IF Value > Max' inside a loop indicate?

It indicates finding the largest value in a set.

What does 'IF Value < 40' with a counter indicate?

It indicates counting a category, e.g., how many values are below a threshold.

What does comparing neighbouring elements and swapping them indicate?

It indicates a bubble sort, sorting the array into order.

Give a sentence template for stating the purpose of an algorithm that inputs n values and outputs the total or average.

It inputs <n> <values> and outputs the total / average of them.

Give a sentence template for stating the purpose of an algorithm that counts values meeting a condition.

It counts how many of the <n> <values> are <condition> and outputs that count.

Give a sentence template for stating the purpose of an algorithm that finds the largest or smallest value.

It finds and outputs the largest / smallest value in the array <Name> and, where relevant, its position.

Give a sentence template for stating the purpose of a search algorithm.

It searches the array <Name> for <SearchItem> and outputs its position, or a message if it is not there.

Give a sentence template for stating the purpose of a sorting algorithm.

It sorts the array <Name> into ascending / descending order.

Give a sentence template for stating the purpose of a validation algorithm.

It validates the input <Name>, rejecting values outside <range> and re-prompting until an acceptable value is entered.

Give a sentence template for stating the purpose of a password check algorithm.

It checks a password against a stored value and allows a maximum of <n> attempts.

In the worked example with 30 marks, what is the purpose?

It inputs 30 marks, then outputs their average and how many of them were below 40.

In the worked example with temperatures, why is Max initialised to Temperature[1]?

So that the algorithm works correctly even if all temperatures are negative, as it starts with the first value rather than 0.

In the validation example, what is the purpose?

It validates the age entered by the user, repeatedly re-prompting until a value between 11 and 18 inclusive is entered.

What is the technical term for the validation check in the age example?

A range check performed by a post-condition loop.

What are the standard methods a candidate must recognise in section 7.4?

Linear search, bubble sort, totalling, counting, and finding maximum, minimum and average values.

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