← IGCSE Computer Science Paper 2

Comments with // (8.1a)

Starts a comment. Everything after // on that line explains the code to people and is ignored when the program runs, so it never changes what the program does.

Part of: IGCSE Computer Science 0478 — 8.1a Data Types and Variables — Module 42

Understanding Comments with // (8.1a) in IGCSE Computer Science Paper 2

What it does: Cambridge pseudocode has no block comment, so each line of a longer comment must begin with //. The comment after // is ignored, so X is still assigned 10 and OUTPUT X displays 10. Comments are written for people to read. The computer ignores everything after // on that line. Comments explain the code but are not run, so adding or removing them never changes the program's behaviour. An end-of-line comment needs // after the code. Without //, the words 'cost of 3 items' would be treated as code and cause an error. The broken line uses / (division) instead of // so the explanation is not a comment. It should be: Score ← 0 // set score to zero.

Common mistakes: Cambridge pseudocode comments start with //, not #. The line should be Score ← 0 // start at zero. A comment needs two forward slashes. A single / is not a comment, so the words would be read as code. It should be // Ask for the user's name.

Class: _____________________ · Name: _____________________ · Date: _________

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This module's key terms are also in a printable crossword (Modules 347–357) and word search (Modules 337–357).

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Learning

Duo

Which line is a correct comment in Cambridge pseudocode?

Store the player's score //// Store the player's score

Matches

Score ← 0 / set score to zero

↓

A single slash does not start a comment. It must be two slashes //, otherwise the text is treated as code and causes an error.

Applying

Meanings

Term

Meaning

Starts a comment. Everything after // on that line explains the code to people and is ignored when the program runs, so it never changes what the program does.

Practice

// Calculate the area of a rectangle

Testing

Gaps

Set the starting score

Check Answer

Spots

2DECLARE Score : INTEGER

3Score ← 0 # start at zero

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Quick Questions

1. Which line is a correct comment in Cambridge pseudocode?

A. Store the player's score //

B. // Store the player's score ✓

A comment starts with //. Everything after the // on that line is the comment, so the // must come before the explanation text.

2. What happens to the text after // when the program runs?

A. It is run as code

B. It is ignored ✓

Comments are written for people to read. The computer ignores everything after // on that line.

3. Which program prints the same output as the other three when the comment is removed? Pick the statement that is true about comments.

A. Adding a comment does not change what the program does ✓

B. Adding a comment changes the value stored in the variable

Comments explain the code but are not run, so adding or removing them never changes the program's behaviour.

4. Which line puts a short comment at the end of a line of code?

A. Total ← Price * 3 // cost of 3 items ✓

B. Total ← Price * 3 cost of 3 items

An end-of-line comment needs // after the code. Without //, the words 'cost of 3 items' would be treated as code and cause an error.

5. A comment needs to explain code that runs over two lines. Which is correct?

A. // Calculate the total cost // including the delivery fee ✓

B. // Calculate the total cost including the delivery fee

Each line of a multi-line comment must start with its own //. The second line without // would be treated as code.

Match the Pairs

// Calculate the area → A comment on its own line that explains the code below it and is ignored when the program runs

Total ← Price * Qty // cost of items → A statement followed by an end-of-line comment: the assignment runs but the comment is ignored

A comment that spans several lines needs // at the start of every line → // Program to find the average // Input three marks and output the mean

Adding a comment does not change what the program does, so the program still outputs 10 → X ← 10 // set X to ten OUTPUT X

Score ← 0 / set score to zero → A single slash does not start a comment. It must be two slashes //, otherwise the text is treated as code and causes an error.

// Ask the user for a name and store it in Name INPUT Name → The second line of the comment is missing //, so it would be treated as code and cause an error.

Key Term

//

Starts a comment. Everything after // on that line explains the code to people and is ignored when the program runs, so it never changes what the program does.

Fill in the Blanks

1. // Set the starting score Score ← 0

Hint: Type the two-slash symbol that starts a comment on its own line before the code.

2. Total ← Price * Quantity // cost of items

Hint: Type the symbol that begins a short comment at the end of a line.

3. // Calculate the area of a rectangle // Width and Height are in cm Area ← Width * Height

Hint: A comment that continues onto a second line must start with the comment symbol again.

4. OUTPUT Total // show the final total

Hint: Type the keyword that displays a value. The comment after it is ignored when the program runs.

5. Lives ← 3 // player starts with 3 lives

Hint: Type the assignment operator that stores the value in the variable. The comment only explains the line.

Spot the Error

Question 1

A // Store the player's score

B DECLARE Score : INTEGER

C Score ← 0 # start at zero

D OUTPUT Score

Line C — Cambridge pseudocode comments start with //, not #. The line should be Score ← 0 // start at zero.

Question 2

A / Ask for the user's name

B DECLARE Name : STRING

C INPUT Name

D OUTPUT "Hello ", Name

Line A — A comment needs two forward slashes. A single / is not a comment, so the words would be read as code. It should be // Ask for the user's name.

Question 3

A CONSTANT Pi ← 3.142

B INPUT Radius

C // Work out the circle area

D // Area ← Pi * Radius ^ 2

E OUTPUT Area

Line D — The // turned the calculation into a comment, so it never runs and Area has no value. The calculation should be Area ← Pi * Radius ^ 2 with no // before it. The comment belongs on its own line above.

Question 4

A DECLARE Lives : INTEGER

B Lives ← // starting lives 3

C OUTPUT Lives

Line B — Everything after // is ignored, so the 3 is now part of the comment and the assignment has no value. The comment must go after the code: Lives ← 3 // starting lives.

Question 5

A // Program: temperature check

B // Written for Year 10

C Converts C to F

D INPUT Celsius

E OUTPUT Celsius * 9 / 5 + 32

Line C — In a multi-line comment, every line must start with //. Without it, this line is treated as code. It should be // Converts C to F.

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