Counting down with a for loop
Name:
Date:
Class:
A
Quick Questions
Shade in the A or B circle for each question.
1. Which for loop counts down from 10 to 1?
2. A countdown starts at 10 and should stop after printing 1. Which condition is correct?
3. What does this loop print? for (let i = 3; i >= 1; i--) { console.log(i); }
4. To count down, the starting value of i should be...
5. Which update makes a for loop count down in steps of 2?
B
Match the Pairs
Draw a line connecting each item on the left to its match on the right.
| Left column | Right column | |
|---|---|---|
| 1for (let i = 10; i >= 1; i--) | Afor (let i = 10; i >= 1; i--) | |
| 2for (let i = 10; i >= 0; i -= 2) | Bfor (let i = 10; i >= 1; i--) { console.log(i); } | |
| 3To count down, the loop condition must use >= so the loop keeps running while the counter is still at or above the last number | CCounts down from 10 to 1, taking away 1 each time the loop repeats | |
| 4A countdown loop updates the counter by subtracting, so the counter gets smaller every time | DThe condition i <= 1 is false straight away because 10 is not less than or equal to 1, so the loop never runs. It should be i >= 1. | |
| 5for (let i = 10; i >= 1; i++) | EThe update i++ adds 1, so the counter goes up away from 1 and the loop never ends. It should be i--. | |
| 6for (let i = 10; i <= 1; i--) | FCounts down from 10 to 0 in steps of 2: 10, 8, 6, 4, 2, 0 |
C
Definitions
for (let i = 10; i >= 1; i--)
D
Fill in the Blanks
Complete each line of code by filling in the missing parts.
1.
for (let i = __; i >= 1; i--) {
console.log(i);
}
2.
for (let i = 10; i __ 1; i--) {
console.log(i);
}
3.
for (let i = 10; i >= 1; ___) {
console.log(i);
}
4.
for (let i = 10; i >= 1; i __ 2) {
console.log(i);
}
5.
for (let i = 10; i >= 1; i--) {
console.log(_);
}
E
Spot the Error
Shade in the letter of the line that contains an error.
Question 1
A
console.log("Countdown");
B
for (let i=10; i>=1; i++) {
C
console.log(i);
D
}
Question 2
A
for (let i=1; i>=10; i--) {
B
console.log(i);
C
}
Question 3
A
let count = 0;
B
for (let i=10; i>=1; i--) {
C
count--;
D
}
E
console.log(count);
Question 4
A
let total = 0;
B
for (let i=10; i>=1; i--) {
C
total += i;
D
console.log(totl);
E
}
Question 5
A
console.log("Evens down");
B
for (let i=10; i>=2; i-=2) {
C
console.log("i");
D
}
Answer Key
Counting down with a for loop
Section A: Quick Questions
Q1
B — for (let i = 10; i >= 1; i--)
Q2
A — i >= 1
Q3
A — 3, 2, 1
Q4
B — High, such as let i = 10
Q5
A — i -= 2
Section B: Match the Pairs
Q1
for (let i = 10; i >= 1; i--) → Counts down from 10 to 1, taking away 1 each time the loop repeats
Q2
for (let i = 10; i >= 0; i -= 2) → Counts down from 10 to 0 in steps of 2: 10, 8, 6, 4, 2, 0
Q3
To count down, the loop condition must use >= so the loop keeps running while the counter is still at or above the last number → for (let i = 10; i >= 1; i--) {
console.log(i);
}
Q4
A countdown loop updates the counter by subtracting, so the counter gets smaller every time → for (let i = 10; i >= 1; i--)
Q5
for (let i = 10; i >= 1; i++) → The update i++ adds 1, so the counter goes up away from 1 and the loop never ends. It should be i--.
Q6
for (let i = 10; i <= 1; i--) → The condition i <= 1 is false straight away because 10 is not less than or equal to 1, so the loop never runs. It should be i >= 1.
Section C: Definitions
Q1
for (let i = 10; i >= 1; i--) — A for loop that counts down: start i high, keep going while i >= 1, and subtract 1 each time with i--. Use i -= 2 to count down in steps of 2.Section D: Fill in the Blanks
Q1
for (let i = 10; i >= 1; i--) {
console.log(i);
}Q2
for (let i = 10; i >= 1; i--) {
console.log(i);
}Q3
for (let i = 10; i >= 1; i--) {
console.log(i);
}Q4
for (let i = 10; i >= 1; i -= 2) {
console.log(i);
}Q5
for (let i = 10; i >= 1; i--) {
console.log(i);
}Section E: Spot the Error
Q1
B — i++ adds 1 each time, so i goes up (11, 12, ...) and i >= 1 stays true forever. A countdown must use i-- to subtract 1 each time.
Q2
A — A countdown must start high. Starting at 1 makes i >= 10 false straight away, so the loop never runs. It should be let i=10 and i>=1.
Q3
C — The loop runs 10 times, and count should go up by 1 each time with count++. Using count-- would give -10 instead of 10.
Q4
D — The variable is spelled total. Writing totl causes a ReferenceError because that name was never created.
Q5
C — Quotes make "i" a piece of text, so the letter i prints every time. Remove the quotes to print the counter value: console.log(i);