Sequence 1 · Topic 3.10 Lists

Trace investigation

About 30 minutes. Pick a version and a test, predict the returned value, then step through the trace one line at a time. Your goal is to find a test that exposes each of the three buggy versions. This is a step-by-step simulation of these four procedures, not a code runner.

1. Choose a version

Version AVersion BVersion CVersion D

Version A is correct. B, C and D each have one planted bug. Read the code to find it.

2. Choose a test

Typical week [4, 0, 12, 7], threshold 5Equal to threshold [5, 3, 5, 9], threshold 5Last reading misses [8, 6, 9, 1], threshold 5Empty list [], threshold 5Your test

Version A with [4, 0, 12, 7], threshold 5

Version A · CountAtLeast

1PROCEDURE CountAtLeast(readings, threshold)2{3  count ← 04  FOR EACH r IN readings5  {6    IF (r ≥ threshold)7    {8      count ← count + 19    }10  }11  RETURN count12}

Bug hunt: find a test that exposes each buggy version

Version B:not exposed yet
Version C:not exposed yet
Version D:not exposed yet

A test counts once you have predicted and run it. Progress lives on this page only and resets when you leave.

Next: Diagnostic check →