← ACARA Digital Technologies Years 7–8

The number data type

A value written without quotes, whole (7), decimal (3.5) or negative (-2), that you can calculate with. 5 is a number but '5' in quotes is a string, which is text.

Part of: ACARA Digital Technologies Years 7–8 — Programming with Control Structures and Functions (JavaScript) — Module 13

Understanding The number data type in ACARA Digital Technologies Years 7–8

What it does: 7 and 3 are numbers, so + adds them and gives 10. The quotes turn 5 into text, so this variable holds a string and not a number. Numbers can be calculated with, so 5 + 5 is 10. Joining two strings, like "5" + "5", gives "55". A whole number has no decimal point. 4.2 is a decimal number. Negative values like -2 are numbers too, as long as they are written without quotes.

Common mistakes: The letter x is not a multiplication operator in JavaScript. Numbers are multiplied with *, so the line should be let total = price * qty;. typeof is one word. Writing 'type of' with a space is a syntax error. It should be console.log(typeof total); which prints number.

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This module's key terms are also in a printable crossword (Modules 562–580) and word search (Modules 522–580).

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Each concept is reinforced from every angle — learned, then applied, then tested.

Learning

Duo

Which one is a number in JavaScript?

let age = 13;let age = "13";

Matches

let age = "13"; console.log(age + 2);

↓

The quotes make "13" a string, so age + 2 joins the text and prints 132 instead of adding to give 15. Remove the quotes: let age = 13;

Applying

Meanings

Term

number

Meaning

A value written without quotes, whole (7), decimal (3.5) or negative (-2), that you can calculate with. 5 is a number but '5' in quotes is a string, which is text.

Practice

let age = 13;

Testing

Gaps

console.log(lives 2);

Check Answer

Spots

2let qty = 4;

3let total = price x qty;

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Quick Questions

1. Which one is a number in JavaScript?

A. let age = "13";

B. let age = 13; ✓

A number is written without quotes. Quotes around 13 turn it into a string, which is text.

2. Which value is a decimal number?

A. 3.5 ✓

B. "3.5"

3.5 is a decimal number. With quotes it becomes a string, so it is only text.

3. Which one is a negative number?

A. let temp = -2; ✓

B. let temp = "-2";

A negative number has a minus sign and no quotes. "-2" in quotes is a string.

4. What does 5 + 5 give?

A. 10 ✓

B. 55

Numbers can be calculated with, so 5 + 5 is 10. Joining two strings, like "5" + "5", gives "55".

5. Which statement is true?

A. 5 and "5" are both numbers

B. 5 is a number and "5" is a string ✓

Quotes make the difference. 5 is a number, but "5" is a string, which is text.

Match the Pairs

let score = 3.5; → Stores a decimal number. It has no quotes, so JavaScript treats it as a number you can calculate with.

let temp = -2; → Stores a negative number. The minus sign is part of the number, and it still has no quotes.

A whole number with no quotes is a number, so you can calculate with it → let total = 7 + 3;

A value in quotes is a string, not a number, even if it looks like a number → let answer = "5";

let age = "13"; console.log(age + 2); → The quotes make "13" a string, so age + 2 joins the text and prints 132 instead of adding to give 15. Remove the quotes: let age = 13;

let price = 3,50; → A decimal number uses a full stop, not a comma. Write let price = 3.50; so it is one number.

Key Term

number

A value written without quotes, whole (7), decimal (3.5) or negative (-2), that you can calculate with. 5 is a number but '5' in quotes is a string, which is text.

Fill in the Blanks

1. let lives = 3; console.log(lives + 2);

Hint: Type the arithmetic operator that adds two numbers, because numbers can be calculated with.

2. // negative number: minus two let change = -2;

Hint: Type the negative number described in the comment, with no quotes.

3. // decimal number: three and a half let price = 3.5;

Hint: Type the decimal number described in the comment, with no quotes.

4. let a = 5; let b = "5"; console.log(typeof a); // number

Hint: Type the name of the variable that holds the number, not the text in quotes.

5. let n = 7; console.log(typeof n); // number

Hint: Type the data type name that typeof reports for a whole number.

Spot the Error

Question 1

A let price = 3.5;

B let qty = 4;

C let total = price x qty;

D console.log(total);

Line C — The letter x is not a multiplication operator in JavaScript. Numbers are multiplied with *, so the line should be let total = price * qty;

Question 2

A let score = 7;

B let bonus = 3;

C let total = score + bonus;

D console.log(type of total);

Line D — typeof is one word. Writing 'type of' with a space is a syntax error. It should be console.log(typeof total); which prints number.

Question 3

A let a = 1.5;

B let b = 2.5;

C let c = 3,5;

D console.log(a + b + c);

Line C — Decimal numbers use a full stop (decimal point), not a comma. A comma here is a syntax error. It should be let c = 3.5;

Question 4

A let n = "5";

B let total = n + 2;

C console.log(total);

Line A — Quotes make "5" a string, which is text. Then n + 2 joins the text and prints 52 instead of adding to make 7. It should be let n = 5;

Question 5

A let big = 1,000;

B let half = big / 2;

C console.log(half);

Line A — Numbers are written without commas. The comma causes a syntax error. It should be let big = 1000;

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