← IGCSE Computer Science Paper 2

Errors in a flowchart

A mistake in a flowchart, such as the wrong symbol shape, a missing Yes or No label, a path that never reaches Stop, or a loop arrow joining the wrong place.

Part of: IGCSE Computer Science 0478 — 7c Pseudocode and Flowcharts — Module 104, ACARA Digital Technologies Years 7–8 — Tracing and Debugging Algorithms — Module 55

Understanding Errors in a flowchart in IGCSE Computer Science Paper 2

What it does: The last flow line ends at an output with no Stop terminator, so the path never reaches Stop and the flowchart is wrong. Symbols should hold short pseudocode such as Total <- Total + Num. Writing a sentence is a flowchart error. Input and output use a parallelogram. A rectangle is the process symbol, used for things like Total ← Total + 1. A decision always has two exits, one labelled Yes and one labelled No. With only one exit, the flowchart cannot show what happens when the answer is different. The loop arrow must return to the decision diamond so the condition is tested again after each repeat. Joining elsewhere breaks the loop.

Common mistakes: Input must be drawn in a parallelogram, not a rectangle. A rectangle is the process symbol. The line should be Para: INPUT Age. The line leaving the decision has no Yes label, so the reader cannot tell when this path is taken. It should be Yes -> Para: OUTPUT Pass.

Class: _____________________  ·  Name: _____________________  ·  Date: _________

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This module's key terms are also in a printable crossword (Modules 242–253) and word search (Modules 232–253).

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Learning
Duo
A student draws a rectangle for the step 'INPUT Age'. Is this correct?
No, input needs a parallelogramYes, every step uses a rectangle
Matches
Decision: Age >= 18 ? with both arrows leaving it unlabelled
↓
The Yes and No labels are missing, so the reader cannot tell which path is taken when the condition is true or false
Applying
Meanings
Term
flowchart error
Meaning
A mistake in a flowchart, such as the wrong symbol shape, a missing Yes or No label, a path that never reaches Stop, or a loop arrow joining the wrong place.
Practice
Terminator: START
Testing
Gaps
INPUT needs a , not a box
Check Answer
Spots
1Oval: Start
2Rect: INPUT Age

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Quick Questions

1. A student draws a rectangle for the step 'INPUT Age'. Is this correct?
A. No, input needs a parallelogram ✓
B. Yes, every step uses a rectangle
Input and output use a parallelogram. A rectangle is the process symbol, used for things like Total ← Total + 1.
2. A flowchart has a diamond with the question 'Age >= 18?'. One arrow leaves it, going down to 'OUTPUT Adult'. What is the error?
A. No error: a decision only needs one arrow out
B. Decision with one exit: it needs two labelled arrows, Yes and No ✓
A decision always has two exits, one labelled Yes and one labelled No. With only one exit, the flowchart cannot show what happens when the answer is different.
3. A flowchart has a Start oval but its last box is 'OUTPUT Total' with no arrow leading on. What is the error?
A. Missing terminator: the path never reaches a Stop oval ✓
B. No error: the output box can end the flowchart
Every path must finish at a Stop terminator (an oval). Without it, the flowchart does not show where the algorithm ends.
4. Which decision diamond is correct?
A. Diamond with 'Mark >= 50?' and two arrows with no labels
B. Diamond with 'Mark >= 50?' and arrows labelled Yes and No ✓
Each exit from a decision must be labelled Yes or No so the reader knows which path to follow.
5. In a WHILE loop flowchart, the arrow after the loop body joins the box after the decision, so the condition is never checked again. What is wrong?
A. The loop arrow joins the wrong place: it must go back to the decision ✓
B. Nothing is wrong: loop arrows can join any later box
The loop arrow must return to the decision diamond so the condition is tested again after each repeat. Joining elsewhere breaks the loop.

Match the Pairs

A rectangle containing: INPUT Age → Wrong symbol shape: input and output belong in a parallelogram, not a process rectangle
A diamond with only one arrow leaving it → A decision with one exit: the diamond needs two labelled exits, Yes and No
A path must finish at a Terminator labelled STOP, so a missing terminator is an error → START -> INPUT Num -> OUTPUT Num * 2 -> (no STOP)
Text in a symbol should be a pseudocode statement, not a sentence → Process box: Work out the total of the numbers
Decision: Age >= 18 ? with both arrows leaving it unlabelled → The Yes and No labels are missing, so the reader cannot tell which path is taken when the condition is true or false
WHILE loop: the arrow from the end of the loop body goes to the box after the loop → The loop arrow joins the wrong place; it should return to the decision at the top of the loop so the condition is checked again

Key Term

flowchart error
A mistake in a flowchart, such as the wrong symbol shape, a missing Yes or No label, a path that never reaches Stop, or a loop arrow joining the wrong place.

Fill in the Blanks

1. INPUT needs a parallelogram, not a box
Hint: Type the name of the shape used for input in a flowchart
2. A decision needs a Yes and a No exit
Hint: Type the label for the second exit from a decision
3. Every path must end at the Stop terminator
Hint: Type the word written in the terminator that ends the flowchart
4. A loop arrow must rejoin before the decision
Hint: Type the name of the symbol where a loop arrow should rejoin
5. Write Total ← Total + Mark, not a sentence
Hint: Type the assignment symbol used in a process box instead of words

Spot the Error

Question 1
A Oval: Start
B Rect: INPUT Age
C Diamond: Age >= 18?
D Yes -> Para: OUTPUT Adult
E No -> Para: OUTPUT Minor
F Oval: Stop
Line B — Input must be drawn in a parallelogram, not a rectangle. A rectangle is the process symbol. The line should be Para: INPUT Age.
Question 2
A Oval: Start
B Para: INPUT Mark
C Diamond: Mark >= 50?
D Para: OUTPUT Pass
E No -> Para: OUTPUT Fail
F Oval: Stop
Line D — The line leaving the decision has no Yes label, so the reader cannot tell when this path is taken. It should be Yes -> Para: OUTPUT Pass.
Question 3
A Oval: Start
B Rect: Count <- 0
C Rect: Add one to the counter
D Para: OUTPUT Count
E Oval: Stop
Line C — Statements inside flowchart symbols must be written as pseudocode, not as a sentence. It should be Rect: Count <- Count + 1.
Question 4
A Rect: Start
B Para: INPUT Price
C Rect: Total <- Price * 1.2
D Para: OUTPUT Total
E Oval: Stop
Line A — Start and Stop must be drawn in a terminator (oval) symbol. A rectangle is the process symbol. It should be Oval: Start.
Question 5
A Oval: Start
B Para: INPUT Score
C Rect: Score > 90?
D Yes -> Para: OUTPUT Top
E No -> Para: OUTPUT Try again
F Oval: Stop
Line C — A decision with a Yes/No question must be drawn as a diamond, not a rectangle. It should be Diamond: Score > 90?.

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