Study guide: Trace and Repair Changing Values
Track counters, assignment order and accumulated totals, then repair misplaced resets.
Ideas to explain in your own words
- Record a variable’s value after each repetition.
- Trace two variables and explain how assignment order changes the result.
- Distinguish the current item from the accumulated total.
- Move initialization outside a loop and retest its total.
Watch your reasoning
- Trace all four additions: 1 → 3 → 5 → 7 → 9. There are four repetitions after the starting value, so the final count is 9.
- b copies the current 4 before a increases to 5. It remains 4 afterward.
- The trace totals are 2, 7, 8. The final 8 includes each list value once.
- Each reset discards the previous sum; the final visit resets to 0 and adds 2. Moving the reset before the loop would instead give 9.
A worked review example
Trace a Repeat with a Counter: Starting at 0 and adding 2 three times gives 0 → 2 → 4 → 6. The shown result is 6; the initial value is not an extra repetition. Watch the Order of Updates: Original rows after both variables are set: (a, b) = (2, 0) → (2, 2) → (5, 2). Reordered updates give (2, 0) → (5, 0) → (5, 5). The original shows 5 and 2. Add a List into One Total: Rows: position 1, item 3, total 3; position 2, item 1, total 4; position 3, item 4, total 8. After the loop the algorithm shows 8. Find a Reset in the Wrong Place: Faulty trace: 0 → 2, reset 0 → 3, reset 0 → 4; shown 4. Repaired trace: 0 → 2 → 5 → 9; shown 9. An empty list visits no items, so the repaired result is 0.
Make a practice plan
- Try the supplied lesson problems without looking at the answers.
- Compare your method with the worked examples and explain any correction.
- Use the new review cases, then complete the transfer task on paper or in your own document.