A function that totals and averages an array
Name:
Date:
Class:
A
Quick Questions
Shade in the A or B circle for each question.
1. Which line should come BEFORE the loop in a function that totals an array?
2. Which line adds each item to the total inside a for...of loop?
3. Where should 'return total;' go in a totalling function?
4. What happens if you write 'let total = 0;' INSIDE the loop?
5. Which expression gives the average of the array nums once total is calculated?
B
Match the Pairs
Draw a line connecting each item on the left to its match on the right.
| Left column | Right column | |
|---|---|---|
| 1let total = 0; | Alet total = 0 is inside the loop, so the total resets to 0 on every pass. It must be declared once before the loop. | |
| 2return total / nums.length; | BSets the running total to 0 before the loop starts, so each array item can be added to it. | |
| 3A loop adds every item in the array to the running total | Ctotal + num works out a value but never stores it. It should be total += num so the total is updated. | |
| 4Check for an empty array first so you never divide by zero | Dfor (const num of nums) { total += num; } | |
| 5for (const num of nums) { let total = 0; total += num; } | EDivides the total by the number of items in the array to give the average. | |
| 6for (const num of nums) { total + num; } | Fif (nums.length === 0) return 0; |
C
Definitions
total += num
D
Fill in the Blanks
Complete each line of code by filling in the missing parts.
1.
function sumArray(nums) {
let total = _;
for (const num of nums) total += num;
2.
for (const num of nums) {
total __ num;
}
3.
let total = 0;
for (const n of nums) total += n;
return total _ nums.length;
4.
if (nums.length ___ 0) {
return 0;
}
5.
const sum = sumArray(nums);
return sum / nums.______;
E
Spot the Error
Shade in the letter of the line that contains an error.
Question 1
A
function sumAll(nums) {
B
let total = 1;
C
for (const n of nums)
D
total += n;
E
return total;
F
}
Question 2
A
function average(nums {
B
let total = 0;
C
for (const n of nums)
D
total += n;
E
return total / nums.length;
F
}
Question 3
A
function addUp(nums) {
B
let total = 0;
C
for (const n of nums)
D
total = n;
E
return total;
F
}
Question 4
A
const average = (nums) -> {
B
let total = 0;
C
for (const n of nums)
D
total += n;
E
return total / nums.length;
F
}
Question 5
A
function sumScores(scores) {
B
const total = 0;
C
for (const s of scores)
D
total += s;
E
return total;
F
}
Answer Key
A function that totals and averages an array
Section A: Quick Questions
Q1
A — let total = 0;
Q2
A — total += num;
Q3
A — After the loop has finished
Q4
B — total resets to 0 on every pass, so the result is wrong
Q5
B — total / nums.length
Section B: Match the Pairs
Q1
let total = 0; → Sets the running total to 0 before the loop starts, so each array item can be added to it.
Q2
return total / nums.length; → Divides the total by the number of items in the array to give the average.
Q3
A loop adds every item in the array to the running total → for (const num of nums) { total += num; }
Q4
Check for an empty array first so you never divide by zero → if (nums.length === 0) return 0;
Q5
for (const num of nums) {
let total = 0;
total += num;
} → let total = 0 is inside the loop, so the total resets to 0 on every pass. It must be declared once before the loop.
Q6
for (const num of nums) {
total + num;
} → total + num works out a value but never stores it. It should be total += num so the total is updated.
Section C: Definitions
Q1
total += num — Adds each array item to a running total inside a loop. Set let total = 0 before the loop, then return total. Divide by nums.length for the average.Section D: Fill in the Blanks
Q1
function sumArray(nums) {
let total = 0;
for (const num of nums) total += num;Q2
for (const num of nums) {
total += num;
}Q3
let total = 0;
for (const n of nums) total += n;
return total / nums.length;Q4
if (nums.length === 0) {
return 0;
}Q5
const sum = sumArray(nums);
return sum / nums.length;Section E: Spot the Error
Q1
B — The running total must start at 0. Starting at 1 makes every answer one too big. It should be let total = 0;
Q2
A — The parameter list is missing its closing bracket. It should be function average(nums) {
Q3
D — Using = replaces the total each time round the loop, so only the last item is kept. It should be total += n; to add each item to the total.
Q4
A — JavaScript arrow functions use => not ->. It should be const average = (nums) => {
Q5
B — total changes inside the loop, so it cannot be declared with const. It should be let total = 0; so it can be updated.