An if statement inside a loop

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Quick Questions

Shade in the A or B circle for each question.

1. Where does the if go so it is checked on every repeat of the loop?

A After the loop's closing brace }

B Inside the loop's curly braces { }

2. for (let i = 1; i <= 5; i++) { if (i > 3) { console.log(i); } } What does this print?

A 4 then 5

B 1 2 3 4 5

3. Which condition checks if the loop counter i is an even number?

A if (i % 2 === 0)

B if (i % 2 = 0)

4. let count = 0; for (let i = 1; i <= 10; i++) { if (i % 2 === 0) { count++; } } What is count at the end?

A 10

B 5

5. To count only the matches in a loop, where should count++ go?

A Inside the if, so it only runs when the test is true

B Inside the loop but outside the if

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 = 1; i <= 10; i++) { if (i % 2 === 0) { count++; } }		Afor (let i = 0; i < scores.length; i++) { if (scores[i] > 50) { passes++; } }
2for (let i = 1; i <= 5; i++) { if (i > 3) { console.log(i); } else { console.log("low"); } }		BPrints low for 1, 2 and 3, then prints the number for 4 and 5, because each pass takes a different branch.
3Count only the scores that are above 50 by putting an if inside the loop.		CChecks every number from 1 to 10 and adds 1 to count only when the number is even.
4Use % 2 inside a loop to tell whether each number is even.		DThe if uses = (assignment) instead of === (comparison), so it does not test whether i is even. It should be i % 2 === 0.
5for (let i = 1; i <= 10; i++) { if (i % 2 = 0) { count++; } }		Efor (let n = 1; n <= 8; n++) { if (n % 2 === 0) { console.log(n); } }
6if (i % 2 === 0) { for (let i = 1; i <= 10; i++) { count++; } }		FThe if is outside the loop, so it is only checked once and every number gets counted. The if must go inside the loop body.

Definitions

for (...) { if (...) { ... } }

Fill in the Blanks

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

for (let n = 1; n <= 6; n++) { __ (n > 3) { console.log(n); } }

for (let i = 1; i <= 10; i++) { if (i _ 2 === 0) { console.log(i); } }

let count = 0; for (let n = 1; n <= 9; n++) { if (n > 5) { _____++; } }

for (let i = 1; i <= 4; i++) { if (i > 2) { console.log("big"); } ____ { console.log("small"); } }

let total = 0; for (let i = 1; i <= 10; i++) { if (i % 2 === 0) { total += _; } }

Spot the Error

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

Question 1

A let matches = 0;

B for (let n = 1; n <= 8; n++) {

C if (n % 2 === 0) {

D matches + 1;

E }

F }

Question 2

A for (let i = 1; i <= 6; i++) {

B if (i % 2 = 0) {

C console.log(i);

D }

E }

Question 3

A let total = 0;

B for (let i = 0; i < 10, i++) {

C if (i > 5) {

D total += i;

E }

F }

Question 4

A for (let i = 1; i <= 5; i++ {

B if (i % 2 === 1) {

C console.log("odd " + i);

D }

E }

Question 5

A for (let i = 1; i <= 4; i++) {

B if (i % 2 === 0) {

C console.log("even);

D } else {

E console.log("odd");

F }

Answer Key

An if statement inside a loop

Section A: Quick Questions

B — Inside the loop's curly braces { }

A — 4 then 5

A — if (i % 2 === 0)

B — 5

A — Inside the if, so it only runs when the test is true

Section B: Match the Pairs

for (let i = 1; i <= 10; i++) { if (i % 2 === 0) { count++; } } → Checks every number from 1 to 10 and adds 1 to count only when the number is even.

for (let i = 1; i <= 5; i++) { if (i > 3) { console.log(i); } else { console.log("low"); } } → Prints low for 1, 2 and 3, then prints the number for 4 and 5, because each pass takes a different branch.

Count only the scores that are above 50 by putting an if inside the loop. → for (let i = 0; i < scores.length; i++) { if (scores[i] > 50) { passes++; } }

Use % 2 inside a loop to tell whether each number is even. → for (let n = 1; n <= 8; n++) { if (n % 2 === 0) { console.log(n); } }

for (let i = 1; i <= 10; i++) { if (i % 2 = 0) { count++; } } → The if uses = (assignment) instead of === (comparison), so it does not test whether i is even. It should be i % 2 === 0.

if (i % 2 === 0) { for (let i = 1; i <= 10; i++) { count++; } } → The if is outside the loop, so it is only checked once and every number gets counted. The if must go inside the loop body.

Section C: Definitions

for (...) { if (...) { ... } } — An if inside a loop body is checked again on every repeat, so each pass can take a different branch, such as counting only the matches.

Section D: Fill in the Blanks

for (let n = 1; n <= 6; n++) {
  if (n > 3) { console.log(n); }
}

for (let i = 1; i <= 10; i++) {
  if (i % 2 === 0) { console.log(i); }
}

let count = 0;
for (let n = 1; n <= 9; n++) {
  if (n > 5) { count++; } }

for (let i = 1; i <= 4; i++) {
  if (i > 2) { console.log("big"); }
  else { console.log("small"); } }

let total = 0;
for (let i = 1; i <= 10; i++) {
  if (i % 2 === 0) { total += i; } }

Section E: Spot the Error

D — matches + 1; works out a value but never stores it, so the counter stays at 0. It should be matches++; to add 1 each time the if is true.

B — A single = assigns a value instead of comparing. The condition should use === so each pass checks whether i is even: if (i % 2 === 0).

B — The parts of a for loop header are separated by semicolons, not commas. It should be for (let i = 0; i < 10; i++) {.

A — The closing bracket of the for loop header is missing. It should be for (let i = 1; i <= 5; i++) {.

C — The string is missing its closing quote. It should be console.log("even"); so the loop can print even on the passes where the if is true.