11.1 Flowchart & Structured English - A-Level Computer Science

Learning Objectives

By the end of this lesson, you will be able to:

Draw basic program flowcharts that demonstrate decision-making processes
Edit and modify given flowcharts to correct errors or improve logic
Design flowcharts to solve specific computational problems
Identify and correctly use flowchart symbols: input/output, decision, terminator, process boxes, subroutine, connector, and flow lines
Identify errors in algorithms and program flowcharts for given scenarios
Create trace tables to follow flowchart execution with test data
Convert between pseudocode, algorithms, and flowchart representations
Implement and write Cambridge-style pseudocode from given flowcharts or structured English
Write pseudocode statements for declaring variables and constants, assignments, expressions, and input/output operations

Key Terms

Flowchart

A diagrammatic way of representing an algorithm used to produce the solution to a problem

Terminator

Symbol used to show where a flowchart begins (START) and where it ends (STOP)

Process Box

Rectangle symbol representing any calculation or variable assignment (uses ← symbol)

Input/Output

Parallelogram shape representing input or output operations (equivalent to INPUT or PRINT)

Decision Box

Diamond shape representing conditional statements (IF) or loops, with Yes/True and No/False branches

Subroutine

Symbol used to call a subroutine from the main flowchart (equivalent to CALL statement)

Flow Line

Arrow lines showing the direction to follow when working through a flowchart

Connector

Circle symbol indicating continuation of a flowchart across multiple pages

Algorithm

A step-by-step procedure or formula for solving a problem

Trace Table

A table used to track variable values and outputs as an algorithm executes step by step

Sequence

The simplest programming construct where instructions are executed one after another

Test Data

Data used to test a program, including normal, abnormal/erroneous, and boundary/extreme cases

Pseudocode

A simplified programming language used to design algorithms, following Cambridge conventions

Structured English

A restricted subset of English used to describe algorithms in a clear, unambiguous way

Flowchart Fundamentals

A program flowchart is a diagrammatic way of representing an algorithm used to produce the solution to a problem. Flowcharts help visualize the logic and flow of a program before writing actual code.

Flowchart Symbols

Standard Flowchart Symbols

START

Terminator

Start/Stop

Process

Process Box

Calculations

INPUT X

Input/Output

Parallelogram

X > 10?

Decision

Diamond

CALL Calc

Subroutine

Call function

Connector

Continuation

Symbol Details:

Terminator: Oval shape showing where flowchart begins and ends
Process Box: Rectangle representing calculations or variable assignments (uses ← symbol)
Input/Output: Parallelogram equivalent to INPUT or PRINT statements
Decision Box: Diamond shape with Yes/True and No/False branches
Subroutine: Symbol used to call a subroutine (equivalent to CALL)
Flow Line: Arrows showing direction through the flowchart
Connector: Circle indicating flowchart continuation across pages

Real-Life Analogy:

Think of a flowchart like a recipe for cooking:

Terminator: "Start cooking" and "Serve meal"
Process Box: "Chop vegetables", "Mix ingredients"
Input/Output: "Add 2 cups of flour", "Taste the sauce"
Decision Box: "Is the pasta cooked?" → Yes/No branches
Subroutine: "Make the sauce" (a separate procedure)
Flow Lines: The order of steps in the recipe

Flowchart Symbols Interactive Guide

Drag and drop flowchart symbols to build a simple algorithm. This simulation helps you understand how different symbols connect to form a complete flowchart.

START

Terminator

INPUT

Input/Output

PROCESS

Process

DECISION

Decision

CALL

Subroutine

Drag symbols here to build your flowchart

How to use: Drag symbols from the palette to the canvas. Connect them in logical order to create algorithms like "Check if a number is positive" or "Calculate average of three numbers".

Example: Weather Decision Flowchart

Flowchart Description:

START
Check the Weather Channel
Decision: Rain Predicted? (Yes/No)
If Yes: Stay Home
If No: Play Golf
STOP

Note:

This is a simple sequence with one decision point. The Weather Channel is a Cable Channel.

START

Check the Weather Channel

(Cable Channel 61)

Rain Predicted?

Yes → Stay Home No → Play Golf

STOP

Real-Life Example: Mobile App Login Flowchart

Most mobile apps use flowcharts to design their user experience. Here's a simplified login process:

START Login Process
User opens app
INPUT username, password
User enters credentials
DECISION: Valid credentials?
Yes → Go to main screen
No → Show error message
DECISION: Remember me checked?
Yes → Save login token
No → Don't save
STOP Login Process

This flowchart helps developers visualize the login process before writing code, ensuring all cases (valid/invalid credentials, remember me option) are handled.

Check Your Understanding: Flowchart Fundamentals

1. What shape is used for a decision box in a flowchart? [1 mark]

Answer

[1 mark] Diamond shape
[Additional] The diamond has two arrows coming out: one for Yes/True and one for No/False

2. What is the purpose of a terminator symbol? [2 marks]

Answer

[1 mark] To show where the flowchart begins (START)
[1 mark] To show where the flowchart ends (STOP)
[Additional] Usually oval-shaped, marks entry and exit points of the algorithm

3. Which flowchart symbol represents input or output operations? [1 mark]

Answer

[1 mark] Parallelogram shape
[Additional] Equivalent to INPUT or PRINT statements in pseudocode

4. When would you use a connector symbol in a flowchart? [2 marks]

Answer

[1 mark] When a flowchart extends over multiple pages
[1 mark] To indicate continuation points between pages
[Additional] Usually a circle with a letter or number inside to match corresponding connectors

5. What is the difference between a process box and an input/output symbol? [2 marks]

Answer

[1 mark] Process box: Rectangle used for calculations and variable assignments (uses ←)
[1 mark] Input/Output: Parallelogram used for reading input or displaying output
[Additional] Example: "X ← Y + Z" goes in process box, "INPUT name" goes in input/output symbol

Drawing and Interpreting Flowcharts

Flowcharts visually represent algorithms. Being able to draw and interpret them is essential for designing, understanding, and debugging programs.

Example: Profit/Loss Calculation

Problem Description:

Read Cost Price (CP) and Selling Price (SP). Determine if there's a profit or loss.

Algorithm Steps:

Read CP
Read SP
If SP > CP then Profit = SP - CP
Otherwise Loss = CP - SP
End

Trace Example:

When CP = 325 and SP = 458:

Condition: Is 458 > 325? → Yes
Profit = 458 - 325 = 133
Result: Profit = Rs. 133

START

Read Cost price (CP)

Input operation

Read Selling price (SP)

Input operation

Is SP > CP?

Yes No

Profit = SP - CP

Process

Loss = CP - SP

Process

END

Activity 1: Trace Table Practice

Complete the trace table for the following flowchart using test data: 9, 7, 3, 12, 6, 4, 15, 2, 8, 5

A	B	C	X	Output
0	0	100
1	9		9
2		7	7
3		3	3
4	12		12
5			6
6			4
7	15		15
8		2	2
9			8
10			5
				15

Flowchart Logic:

Start with A=0, B=0, C=100
Repeat until A >= 10:
  Input X
  If X > B then B = X
  If X < C then C = X
  A = A + 1
Output B, C

Solution:

A	B	C	X	Output
0	0	100
1	9	9	9
2	9	7	7
3	9	3	3
4	12	3	12
5	12	3	6
6	12	3	4
7	15	3	15
8	15	2	2
9	15	2	8
10	15	2	5
				15, 2

Explanation: The algorithm finds the maximum (B) and minimum (C) values from 10 inputs. B tracks the highest value seen, C tracks the lowest. Final output is B=15, C=2.

Flowchart with Subroutine

Pseudocode:

INPUT width, height
// type in the height and width of the triangle
CALL triangle (width, height)
// this would print out the area
INPUT number
// type in the number of walls
count ← 0
WHILE count < number
    INPUT length, height
    count ← count + 1
    CALL rectangle (length, height)
ENDWHILE

What this algorithm does:

Calculates area of one triangle using subroutine
Then calculates areas of multiple rectangles using a loop
Uses a WHILE loop with counter (count)
Demonstrates subroutine calls within a flowchart

START

INPUT width, height

CALL triangle(width, height)

Subroutine

INPUT number

count ← 0

count < number?

Yes No → STOP

INPUT length, height

count ← count + 1

CALL rectangle(length, height)

Subroutine

Activity 2: Draw a Flowchart

Draw a flowchart to add up five numbers.

Pseudocode provided:

Declare Num, total, count : Integer
Count ← 0
Total ← 0
While count < 5 Do
    Count ← Count + 1
    Total ← Total + Num
Endwhile
Output "Sum of 5 numbers is " Total

Note: There's an error in the pseudocode - it should INPUT Num inside the loop!

Draw the correct flowchart that:

Initializes count and total to 0
Uses a loop to input 5 numbers
Adds each number to the total
Outputs the final sum

Solution Flowchart:

START

count ← 0

total ← 0

count < 5?

Yes No

INPUT number

Get next number

total ← total + number

Add to sum

count ← count + 1

Increment counter

PRINT total

Output result

STOP

Key points: The loop continues while count < 5 (0-4 = 5 iterations). We INPUT a number inside the loop, add it to total, then increment count. The pseudocode is missing the INPUT statement inside the loop.

Real-Life Example: Online Shopping Checkout Flowchart

Most e-commerce websites use complex flowcharts to design their checkout process:

START Checkout
User clicks checkout button
DECISION: User logged in?
No → CALL Login_Process()
Yes → Continue
INPUT shipping address
DECISION: Address valid?
No → Show error, retry
Yes → Continue
INPUT payment details
CALL Process_Payment()
DECISION: Payment successful?
No → Show error, retry
Yes → Generate order confirmation
STOP Checkout

This flowchart ensures all cases are handled: user authentication, address validation, payment processing, and error handling.

Check Your Understanding: Drawing & Interpreting

1. What does the following flowchart find? [2 marks]
Start → A=0, B=0, C=100 → Loop: Input X → If X>B then B=X → If X=10 → Output B,C

Answer

[1 mark] Finds the maximum value (stored in B) from 10 inputs
[1 mark] Finds the minimum value (stored in C) from 10 inputs
[Additional] B starts at 0, C starts at 100. After processing 10 numbers, B contains the highest, C contains the lowest.

2. What is wrong with the pseudocode in the "Add up five numbers" example? [2 marks]

Answer

[1 mark] There is no INPUT statement to read the numbers
[1 mark] The variable "Num" is used in the calculation but never assigned a value
[Additional] Corrected version should have "INPUT Num" inside the while loop before adding to total

3. How many times will the loop execute in the triangle/rectangle example? [2 marks]
count ← 0, WHILE count < number, ... , count ← count + 1

Answer

[1 mark] The loop executes "number" times
[1 mark] Count starts at 0, increments by 1 each time, loop continues while count < number
[Additional] If number=5: count=0,1,2,3,4 (5 iterations). When count=5, condition fails, loop stops.

4. What would be the output of the profit/loss flowchart with CP=200, SP=150? [2 marks]

Answer

[1 mark] Condition: Is SP > CP? 150 > 200? → No
[1 mark] Loss = CP - SP = 200 - 150 = 50
[Additional] Since selling price (150) is less than cost price (200), there's a loss of 50.

5. Identify three types of test data [3 marks]

Answer

[1 mark] Normal test data
[1 mark] Abnormal / erroneous / invalid test data
[1 mark] Boundary / extreme test data
[Additional] 5: "A programmer can use three types of test data when testing a program"

Exam-Style Flowchart Questions

Exam questions often ask you to draw flowcharts based on algorithm descriptions or identify errors in given flowcharts.

Example: Prime Number Counter

Algorithm Description:

Input an integer value.
Jump to step 6 if the value is less than zero.
Call the function IsPrime() using the integer value as a parameter.
Keep a count of the number of times function IsPrime() returns TRUE.
Repeat from step 1.
Output the value of the count with a suitable message.

What this algorithm does:

Continuously reads integers until a negative number is entered
For each non-negative number, checks if it's prime using IsPrime() function
Counts how many prime numbers were entered
When a negative number is entered, stops and outputs the count
Uses a sentinel value (negative number) to terminate input

START

Set Count to 0

Initialize counter

INPUT NextNum

Get number from user

Is NextNum < 0?

Yes No

Set Answer to IsPrime(NextNum)

Call subroutine

Is Answer = TRUE?

Yes No

Set Count to Count + 1

Increment if prime

OUTPUT "Answer is" & Count

Final output

END

Common Flowchart Errors to Avoid

Structural Errors:

Missing terminators - No START or STOP symbols
Incorrect symbol shapes - Using rectangle for decision or parallelogram for process
Unconnected flow lines - Gaps between symbols
Crossing flow lines - Makes the flowchart hard to follow
Missing decision branches - Only showing Yes or No path, not both

Logic Errors:

Infinite loops - No way to exit the loop
Incorrect loop conditions - Wrong comparison or counter update
Missing initialization - Variables not set before use
Wrong order of operations - Processing before input or vice versa
Off-by-one errors - Looping one time too many or too few

Exam Tip: How to Check Your Flowchart

Trace with sample data - Walk through with simple test values
Check all paths - Ensure every Yes/No branch leads somewhere valid
Verify loop exit - Make sure loops can terminate
Test boundary cases - What happens with minimum/maximum values?
Use correct symbols - Examiners check symbol shapes carefully

Exam Question Practice

Exam-Style Question: A school library system needs a flowchart for checking out books. The process is:

Algorithm:

Start
Input StudentID and BookID
Check if StudentID is valid (call ValidateStudent subroutine)
If invalid, output "Invalid Student ID" and stop
Check if BookID is available (call CheckAvailability subroutine)
If not available, output "Book not available" and stop
Update records (call UpdateRecords subroutine)
Output "Book checked out successfully"
Stop

Draw a flowchart for this library checkout system. Include all symbols: terminators, input/output, decisions, process boxes, and subroutines.

Solution Flowchart:

START

INPUT StudentID, BookID

CALL ValidateStudent(StudentID)

Subroutine

Valid Student?

No Yes

OUTPUT "Invalid Student ID"

Error message

CALL CheckAvailability(BookID)

Subroutine

Book Available?

No Yes

OUTPUT "Book not available"

Error message

CALL UpdateRecords()

Subroutine

OUTPUT "Book checked out successfully"

STOP

Key features: Uses three subroutines (ValidateStudent, CheckAvailability, UpdateRecords). Has two decision points with error handling. Shows both successful and unsuccessful paths. All symbols are correctly shaped.

Converting Between Flowcharts and Pseudocode

Flowchart Symbol → Pseudocode

Flowchart Symbol	Pseudocode Equivalent
Terminator (START/STOP)	Beginning/end of algorithm
Input/Output (Parallelogram)	INPUT or OUTPUT/PRINT statements
Process Box (Rectangle)	Assignment statements (variable ← value)
Decision (Diamond)	IF...THEN...ELSE or WHILE conditions
Subroutine	CALL statement
Flow Lines	Sequence of execution

Example Conversion:

// Flowchart: Add two numbers
START
INPUT num1
INPUT num2
sum ← num1 + num2
OUTPUT sum
STOP
// Pseudocode equivalent:
INPUT num1
INPUT num2
sum ← num1 + num2
OUTPUT sum

Check Your Understanding: Exam Preparation

1. In the prime number counter algorithm, what triggers the output? [2 marks]

Answer

[1 mark] When a negative number is input
[1 mark] The negative number acts as a sentinel value to terminate input
[Additional] The algorithm says: "Jump to step 6 if the value is less than zero"

2. What type of loop is used in the "Add up five numbers" flowchart? [1 mark]

Answer

[1 mark] Count-controlled loop (WHILE loop with counter)
[Additional] The loop executes exactly 5 times, controlled by "count < 5" condition

3. Why is initialization important in flowcharts? [2 marks]

Answer

[1 mark] Ensures variables start with known values before use
[1 mark] Prevents errors from uninitialized variables (garbage values)
[Additional] Example: In "Add five numbers", total must start at 0 before adding numbers

4. How would you modify the profit/loss flowchart to handle zero profit? [2 marks]

Answer

[1 mark] Change decision from "SP > CP" to "SP >= CP"
[1 mark] Or add another decision: If SP = CP then output "No profit, no loss"
[Additional] Current flowchart treats SP = CP as loss (since SP > CP is false), which is incorrect

5. What is the purpose of a trace table? [2 marks]

Answer

[1 mark] To track variable values as an algorithm executes step by step
[1 mark] To verify algorithm correctness and identify logic errors
[Additional] Used for debugging and understanding how algorithms work with specific test data

Cambridge Pseudocode Implementation

Cambridge pseudocode is a standardized way to represent algorithms using a structured, programming-like syntax that follows Cambridge International conventions. It bridges the gap between flowcharts/structured English and actual programming code.

Cambridge Pseudocode Syntax Rules

1. Declaration and Initialization

// Constants (values that don't change)
CONSTANT MaxScore = 100
CONSTANT Pi = 3.14159
// Variables (values that can change)
DECLARE score : INTEGER
DECLARE name : STRING
DECLARE price : REAL
DECLARE isPassed : BOOLEAN
// Combined declaration and initialization
DECLARE counter : INTEGER ← 0
DECLARE total : REAL ← 0.0

2. Assignment Statements

// Basic assignment using ←
counter ← 1
total ← price * quantity
average ← sum / count
isValid ← TRUE
// Increment/Decrement
counter ← counter + 1
score ← score - 5

3. Expressions with Operators

// Arithmetic operators
sum ← a + b
difference ← x - y
product ← num1 * num2
quotient ← numerator / denominator
remainder ← number MOD 2
// Logical operators (AND, OR, NOT)
isPass ← (score > = 50) AND (attendance >= 75)
canProceed ← (age > = 18) OR (parentApproval = TRUE)
isInvalid ← NOT (isValid)
// Comparison operators
isGreater ← a > b
isEqual ← x = y
isNotEqual ← value ! = 0

4. Input and Output Statements

// Input from keyboard
INPUT username
INPUT age
INPUT score1, score2, score3
// Output to console
OUTPUT "Hello, World!"
OUTPUT "Your score is: ", score
PRINT "Average = ", average
// Example: Complete program
DECLARE radius, area : REAL
CONSTANT Pi = 3.14159
INPUT radius
area ← Pi * radius * radius
OUTPUT "Area of circle = ", area

Structured English for Algorithm Design

What is Structured English?

Structured English is a restricted subset of English used to describe algorithms in a clear, unambiguous way. It uses:

Imperative verbs (Read, Write, Calculate, If, While, Repeat)
Clear, simple sentences
Indentation to show structure
Standardized keywords

Example: Structured English for Finding Maximum

1. Start
2. Read three numbers: num1, num2, num3
3. Set max to num1
4. If num2 > max then set max to num2
5. If num3 > max then set max to num3
6. Output "Maximum is: " followed by max
7. End

Converting to Cambridge Pseudocode

// Converted from Structured English
DECLARE num1, num2, num3, max : INTEGER
INPUT num1, num2, num3
max ← num1
IF num2 > max THEN
    max ← num2
ENDIF
IF num3 > max THEN
    max ← num3
ENDIF
OUTPUT "Maximum is: ", max

Practice: Convert Flowchart to Cambridge Pseudocode

Convert this flowchart to Cambridge pseudocode:

START

INPUT age

age >= 18?

Yes No

OUTPUT "Adult"

OUTPUT "Minor"

STOP

Write the complete Cambridge pseudocode including variable declaration, input, decision logic, and output.

Solution:

// Age classification program
DECLARE age : INTEGER
INPUT age
IF age >= 18 THEN
    OUTPUT "Adult"
ELSE
    OUTPUT "Minor"
ENDIF

Marking points: Correct variable declaration [1], proper INPUT statement [1], correct IF condition [1], appropriate OUTPUT statements [1], proper indentation and ENDIF [1].

Practice: Structured English to Pseudocode

Convert this Structured English algorithm to Cambridge pseudocode:

1. Start
2. Read a number
3. If the number is greater than 0
4.     Output "Positive"
5. Else if the number is less than 0
6.     Output "Negative"
7. Else
8.     Output "Zero"
9. End

Write the complete Cambridge pseudocode with proper indentation and syntax.

Solution:

// Number classification program
DECLARE number : INTEGER
INPUT number
IF number > 0 THEN
    OUTPUT "Positive"
ELSEIF number < 0 THEN
    OUTPUT "Negative"
ELSE
    OUTPUT "Zero"
ENDIF

Key features: Uses ELSEIF for multiple conditions, proper indentation for readability, correct comparison operators, and ENDIF to close the conditional block.

Check Your Understanding: Cambridge Pseudocode

1. Write Cambridge pseudocode to declare a constant called VAT_RATE with value 0.2 and a variable called price of type REAL. [2 marks]

Answer

CONSTANT VAT_RATE = 0.2
DECLARE price : REAL

[1 mark] Correct constant declaration using CONSTANT keyword
[1 mark] Correct variable declaration with REAL type

2. Write a Cambridge pseudocode assignment statement to calculate total price including VAT. [2 marks]

Answer

totalPrice ← price + (price * VAT_RATE)

[1 mark] Correct use of assignment operator (←)
[1 mark] Correct calculation including parentheses for order of operations

3. Write Cambridge pseudocode to input a student's mark and output "Pass" if mark ≥ 50, otherwise output "Fail". [4 marks]

Answer

DECLARE mark : INTEGER
INPUT mark
IF mark >= 50 THEN
    OUTPUT "Pass"
ELSE
    OUTPUT "Fail"
ENDIF

[1 mark] Correct variable declaration
[1 mark] Correct INPUT statement
[1 mark] Correct IF condition with comparison operator
[1 mark] Proper OUTPUT statements in both branches

4. Write a logical expression in Cambridge pseudocode to check if a number is between 10 and 20 inclusive. [2 marks]

Answer

isInRange ← (number >= 10) AND (number <= 20)

[1 mark] Correct use of AND operator
[1 mark] Correct comparison operators (>= and <= for inclusive range)

5. Convert this Structured English to Cambridge pseudocode: [4 marks]
"Read three numbers, calculate their average, and output the result."

Answer

// Calculate average of three numbers
DECLARE num1, num2, num3, average : REAL
INPUT num1, num2, num3
average ← (num1 + num2 + num3) / 3
OUTPUT "Average = ", average

[1 mark] Correct variable declarations
[1 mark] Correct INPUT statement for three values
[1 mark] Correct calculation with parentheses
[1 mark] Correct OUTPUT statement

Key Takeaways

Flowcharts are diagrammatic representations of algorithms using standardized symbols
Terminator (oval) shows START and STOP points of the algorithm
Process box (rectangle) represents calculations and variable assignments (uses ← symbol)
Input/Output (parallelogram) represents INPUT or PRINT operations
Decision box (diamond) represents conditional statements with Yes/True and No/False branches
Subroutine symbol indicates a call to another procedure or function
Flow lines (arrows) show the direction of execution through the flowchart
Connector (circle) indicates continuation of a flowchart across multiple pages
Trace tables help track variable values and verify algorithm correctness
Three types of test data: Normal, Abnormal/Erroneous, and Boundary/Extreme
Common errors include missing terminators, incorrect symbols, infinite loops, and uninitialized variables
Cambridge pseudocode syntax uses DECLARE for variables, CONSTANT for constants, ← for assignment, and INPUT/OUTPUT for I/O operations
Arithmetic operators (+, -, *, /, MOD) and logical operators (AND, OR, NOT) are used in expressions
Structured English is a clear, unambiguous way to describe algorithms using imperative verbs
Flowcharts, pseudocode, and structured English are interchangeable representations that can be converted between each other
Exam questions often require converting between different algorithm representations
Real-world applications include login systems, e-commerce checkouts, and mobile app workflows

Question Bank

1. Draw a flowchart for an algorithm that inputs three numbers and outputs the largest. [6 marks]

Marking Scheme & Answer

START

INPUT num1, num2, num3

num1 > num2?

Yes No

max ← num1

max > num3?

Yes No

OUTPUT max

max ← num3

OUTPUT max

max ← num2

max > num3?

Yes No

OUTPUT max

max ← num3

OUTPUT max

STOP

Alternative simpler solution: Compare num1 and num2, store larger in max. Then compare max with num3. If num3 > max, update max. Output max.

2. Identify errors in the following flowchart description: [5 marks]
"Start → Input X → If X>10 then Output 'Large' → Process: Y←X+5 → Output Y → Stop"

Marking Scheme & Answer

[1 mark] Decision box missing "No" branch - what happens if X ≤ 10?
[1 mark] Output 'Large' should be in output symbol (parallelogram), not decision box
[1 mark] Process box (Y←X+5) should be rectangle, not just "Process:"
[1 mark] Output Y should be separate output symbol
[1 mark] Missing symbols: Need actual flowchart symbols with correct shapes
[Additional] Corrected: START → Input X (parallelogram) → X>10? (diamond) → Yes: Output 'Large' (parallelogram) → No: (could go directly to next step) → Y←X+5 (rectangle) → Output Y (parallelogram) → STOP

3. Create a trace table for this algorithm with inputs: 5, 12, 8, -1 [6 marks]
total ← 0
count ← 0
REPEAT
  INPUT number
  IF number > 0 THEN
    total ← total + number
    count ← count + 1
  ENDIF
UNTIL number < 0
average ← total / count
OUTPUT average

Marking Scheme & Answer

Iteration	number	total	count	average	Output
Initial	-	0	0	-	-
1	5	5	1	-	-
2	12	17	2	-	-
3	8	25	3	-	-
4	-1	25	3	8.33	8.33

Explanation: The algorithm calculates average of positive numbers until a negative is entered. With inputs 5, 12, 8, -1: total = 5+12+8 = 25, count = 3, average = 25/3 ≈ 8.33. The negative number (-1) triggers loop exit but is not added to total.

4. Convert this pseudocode to a flowchart: [5 marks]
INPUT age
IF age >= 18 THEN
  OUTPUT "Adult"
ELSE
  IF age >= 13 THEN
    OUTPUT "Teenager"
  ELSE
    OUTPUT "Child"
  ENDIF
ENDIF

Marking Scheme & Answer

START

INPUT age

age >= 18?

Yes No

OUTPUT "Adult"

age >= 13?

Yes No

OUTPUT "Teenager"

OUTPUT "Child"

STOP

Key points: Nested IF structure. First checks if adult (≥18). If not, checks if teenager (13-17). If not, must be child (<13). All outputs in parallelogram symbols, decisions in diamonds.

5. Draw a flowchart for a simple calculator that: [6 marks]
- Inputs two numbers and an operator (+, -, *, /)
- Performs the calculation
- Outputs the result
- For division, check for divide by zero error

Marking Scheme & Answer

START

INPUT num1, num2, operator

operator = '/'?

Yes No

num2 = 0?

Yes No

OUTPUT "Error: Division by zero"

result ← num1 / num2

OUTPUT result

operator = '+'?

Yes: result ← num1 + num2 No

operator = '-'?

Yes: result ← num1 - num2 No

operator = '*'?

Yes: result ← num1 * num2 No

OUTPUT "Invalid operator"

STOP

Alternative approach: Use CASE structure or nested IFs. Key elements: Check for division by zero before calculating, handle all four operators, provide error messages for invalid operator or division by zero.

6. What is the difference between a connector and a subroutine symbol? [3 marks]

Marking Scheme & Answer

[1 mark] Connector: Circle symbol used when flowchart continues on another page
[1 mark] Subroutine: Rectangle with extra lines (or dashed) representing a call to another procedure
[1 mark] Connector connects parts of same flowchart, subroutine calls separate algorithm
[Additional] Example: Connector A on page 1 connects to Connector A on page 2. Subroutine CALL triangle(width,height) executes triangle calculation procedure.

7. Explain why flowcharts are useful in programming. [4 marks]

Marking Scheme & Answer

[1 mark] Visual representation makes algorithms easier to understand
[1 mark] Helps identify logic errors before coding
[1 mark] Standard symbols provide clear communication between programmers
[1 mark] Useful for documentation and explaining program logic to others
[Additional] Particularly helpful for complex algorithms with multiple decisions and loops

8. Write Cambridge pseudocode for finding factorial of a number. [5 marks]

Marking Scheme & Answer

// Factorial calculation program
DECLARE n, factorial, i : INTEGER
INPUT n
factorial ← 1
FOR i ← 1 TO n
    factorial ← factorial * i
NEXT i
OUTPUT "Factorial of ", n, " is ", factorial

Alternative using WHILE loop:
DECLARE n, factorial, i : INTEGER
INPUT n
factorial ← 1
i ← 1
WHILE i <= n
factorial ← factorial * i
i ← i + 1
ENDWHILE
OUTPUT "Factorial of ", n, " is ", factorial

9. Write Structured English for an algorithm that checks if a number is prime. [4 marks]

Marking Scheme & Answer

1. Start
2. Input a number n
3. If n is less than 2 then output "Not prime" and end
4. Set divisor to 2
5. Set isPrime to TRUE
6. While divisor is less than n
7.     If n divided by divisor has remainder 0 then
8.         Set isPrime to FALSE
9.     End if
10.     Increment divisor by 1
11. End while
12. If isPrime is TRUE then output "Prime"
13. Else output "Not prime"
14. End

Note: This is basic prime checking. More efficient versions check only up to √n or skip even numbers.

10. Convert this flowchart to Cambridge pseudocode: [6 marks]
Start → Input username, password → Valid? → Yes: Output "Access granted" → No: Output "Access denied" → Stop

Marking Scheme & Answer

// Simple login system
DECLARE username, password : STRING
DECLARE isValid : BOOLEAN
CONSTANT CORRECT_USERNAME = "admin"
CONSTANT CORRECT_PASSWORD = "password123"
INPUT username, password
isValid ← (username = CORRECT_USERNAME) AND (password = CORRECT_PASSWORD)
IF isValid = TRUE THEN
    OUTPUT "Access granted"
ELSE
    OUTPUT "Access denied"
ENDIF

Alternative simpler version: Without constants and Boolean variable:
DECLARE username, password : STRING
INPUT username, password
IF username = "admin" AND password = "password123" THEN
OUTPUT "Access granted"
ELSE
OUTPUT "Access denied"
ENDIF

Learning Objectives

Key Terms

Flowchart

Terminator

Process Box

Input/Output

Decision Box

Subroutine

Flow Line

Connector

Algorithm

Trace Table

Sequence

Test Data

Pseudocode

Structured English

Flowchart Fundamentals

Flowchart Symbols

Standard Flowchart Symbols

Symbol Details:

Real-Life Analogy:

Flowchart Symbols Interactive Guide

Example: Weather Decision Flowchart

Flowchart Description:

Real-Life Example: Mobile App Login Flowchart

Check Your Understanding: Flowchart Fundamentals

1. What shape is used for a decision box in a flowchart? [1 mark]

Answer

2. What is the purpose of a terminator symbol? [2 marks]

Answer

3. Which flowchart symbol represents input or output operations? [1 mark]

Answer

4. When would you use a connector symbol in a flowchart? [2 marks]

Answer

5. What is the difference between a process box and an input/output symbol? [2 marks]

Answer

Drawing and Interpreting Flowcharts

Example: Profit/Loss Calculation

Problem Description:

Trace Example:

Activity 1: Trace Table Practice

Solution:

Flowchart with Subroutine

Pseudocode:

What this algorithm does:

Activity 2: Draw a Flowchart

Pseudocode provided:

Solution Flowchart:

Real-Life Example: Online Shopping Checkout Flowchart

Check Your Understanding: Drawing & Interpreting

1. What does the following flowchart find? [2 marks] Start → A=0, B=0, C=100 → Loop: Input X → If X>B then B=X → If X=10 → Output B,C

Answer

2. What is wrong with the pseudocode in the "Add up five numbers" example? [2 marks]

Answer

3. How many times will the loop execute in the triangle/rectangle example? [2 marks] count ← 0, WHILE count < number, ... , count ← count + 1

Answer

4. What would be the output of the profit/loss flowchart with CP=200, SP=150? [2 marks]

Answer

5. Identify three types of test data [3 marks]

Answer

Exam-Style Flowchart Questions

Example: Prime Number Counter

Algorithm Description:

What this algorithm does:

Common Flowchart Errors to Avoid

Structural Errors:

Logic Errors:

Exam Tip: How to Check Your Flowchart

Exam Question Practice

Algorithm:

Solution Flowchart:

Converting Between Flowcharts and Pseudocode

Flowchart Symbol → Pseudocode

Example Conversion:

Check Your Understanding: Exam Preparation

1. In the prime number counter algorithm, what triggers the output? [2 marks]

Answer

2. What type of loop is used in the "Add up five numbers" flowchart? [1 mark]

Answer

3. Why is initialization important in flowcharts? [2 marks]

1. What does the following flowchart find? [2 marks]
Start → A=0, B=0, C=100 → Loop: Input X → If X>B then B=X → If X=10 → Output B,C

3. How many times will the loop execute in the triangle/rectangle example? [2 marks]
count ← 0, WHILE count < number, ... , count ← count + 1

5. Convert this Structured English to Cambridge pseudocode: [4 marks]
"Read three numbers, calculate their average, and output the result."

2. Identify errors in the following flowchart description: [5 marks]
"Start → Input X → If X>10 then Output 'Large' → Process: Y←X+5 → Output Y → Stop"

3. Create a trace table for this algorithm with inputs: 5, 12, 8, -1 [6 marks]
total ← 0
count ← 0
REPEAT
INPUT number
IF number > 0 THEN
total ← total + number
count ← count + 1
ENDIF
UNTIL number < 0
average ← total / count
OUTPUT average

4. Convert this pseudocode to a flowchart: [5 marks]
INPUT age
IF age >= 18 THEN
OUTPUT "Adult"
ELSE
IF age >= 13 THEN
OUTPUT "Teenager"
ELSE
OUTPUT "Child"
ENDIF
ENDIF

5. Draw a flowchart for a simple calculator that: [6 marks]
- Inputs two numbers and an operator (+, -, *, /)
- Performs the calculation
- Outputs the result
- For division, check for divide by zero error

10. Convert this flowchart to Cambridge pseudocode: [6 marks]
Start → Input username, password → Valid? → Yes: Output "Access granted" → No: Output "Access denied" → Stop