Loops over lists — App development for students

Developer's tip

One by one — “the loop visits positions 0, 1, 2 … up to the last item”

1. for (let i = 0; i < list.length; i++) visits every item, from position 0.
2. Total: add each item. Count: add 1 when the test is true. Best: keep the biggest so far.
3. The body runs once per item: a list of 5 runs it 5 times.

Use it for: Adding scores, counting passes, finding high scores and showing lists of names.

Worked example: 🔁 What number does this code show?
let steps = [8, 15, 13, 9];
let total = 0;
for (let i = 0; i < steps.length; i++) {
  total = total + steps[i];
}
show(total); → 45

✏️ Practice

Work it out in your head or on paper, type the answer and press Check. Stuck? Press “Show me how”.

🏁 Lesson 19 test

20 questions. Check each answer, then go to the next one. Get 16 or more right to pass.

🏅 Sign in with Google to earn the 🔁 List Loop Runner badge when you pass — and a certificate when you finish all 8 lessons of Part 3 · Logic and Building. You can still take the test without signing in.

🖨️ App Dev Worksheet: Loops over Lists

• Worksheet set 1 (PDF)
• Worksheet set 2 (PDF)
• Worksheet set 3 (PDF)