Shorthand updates: +=, -= and ++

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Date:

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Quick Questions

Shade in the A or B circle for each question.

1. Which line does the same job as total = total + price;?

A total += price;

B total =+ price;

2. What does count++; do to the variable count?

A Adds 2 to count

B Adds 1 to count

3. Which statement takes 1 away from lives?

A lives--;

B lives-;

4. let score = 10; score += 5; What is score now?

A 15

B 5

5. Which is the same as x = x + 1;?

A x+1;

B x++;

Match the Pairs

Draw a line connecting each item on the left to its match on the right.

Left column		Right column
1total += price;		Acount+ is not a valid operator. To add 1 you need two plus signs, count++, or you can write count += 1.
2count--;		Bcount++;
3Add 1 to the variable count using the shortest form		CThe symbols are the wrong way round. =+ just assigns a positive price to total instead of adding it. It should be +=.
4Write score = score - 5 in its shorthand form		Dscore -= 5;
5total =+ price;		EAdds the value of price to total and stores the answer back in total
6let count = 0; count+;		FTakes 1 away from count

Definitions

total += price

Fill in the Blanks

Complete each line of code by filling in the missing parts.

let total = 0; total __ 5; console.log(total);

let lives = 3; lives__; console.log(lives);

let count = 0; count = _____ + 1; count++;

const price = 8; let money = 20; money __ price;

const price = 6; let total = 0; _____ += price;

Spot the Error

Shade in the letter of the line that contains an error.

Question 1

A const count = 0;

B count++;

C console.log(count);

Question 2

A let total = 10;

B total =+ 5;

C console.log(total);

Question 3

A let score = 0;

B score += 10;

C score+;

D console.log(score);

Question 4

A let total;

B total += 4;

C total += 6;

D console.log(total);

Question 5

A let lives = 3;

B lives =- 1;

C console.log(lives);

Answer Key

Shorthand updates: +=, -= and ++

Section A: Quick Questions

A — total += price;

B — Adds 1 to count

A — lives--;

A — 15

B — x++;

Section B: Match the Pairs

total += price; → Adds the value of price to total and stores the answer back in total

count--; → Takes 1 away from count

Add 1 to the variable count using the shortest form → count++;

Write score = score - 5 in its shorthand form → score -= 5;

total =+ price; → The symbols are the wrong way round. =+ just assigns a positive price to total instead of adding it. It should be +=.

let count = 0; count+; → count+ is not a valid operator. To add 1 you need two plus signs, count++, or you can write count += 1.

Section C: Definitions

total += price — A shorthand update. Operators like +=, -=, ++ and -- change a variable using its own value, so total += price means total = total + price. count++ adds 1 and count-- takes away 1.

Section D: Fill in the Blanks

let total = 0;
total += 5;
console.log(total);

let lives = 3;
lives--;
console.log(lives);

let count = 0;
count = count + 1;
count++;

const price = 8;
let money = 20;
money -= price;

const price = 6;
let total = 0;
total += price;

Section E: Spot the Error

A — A const variable cannot be changed, so count++ would cause a TypeError. Use let count = 0; for a variable that gets updated.

B — The operator is += (plus first, then equals). =+ just assigns positive 5, so total becomes 5 instead of 15. It should be total += 5;

C — The increase operator needs two plus signs. A single + is a syntax error. It should be score++;

A — Without a starting value, total is undefined, and undefined + 4 gives NaN. A running total must start at 0: let total = 0;

B — The operator is -= (minus first, then equals). =- assigns -1, so lives becomes -1 instead of 2. It should be lives -= 1;