Lab 4 · Decision-Making

Module 4 · Lectures L07–L08 · Week 4 · 120 minutes · guided/independent 70/30

Prerequisites: completion of Labs 1–3 (Lab 1: none). Bring your laptop with the course toolchain verified (see § 3) and your exercise notebook.

2. Learning objectives

By the end of this lab you can:

• Write decision tables before if-statements
• Order ladder branches so the most specific test runs first
• Translate if/else chains to switch and back
• Guard division and input ranges with early exits

These deliver the module's outcomes (PF codes in ../../LEARNING_OUTCOMES.md).

3. Required software and compiler

• Compiler contract: g++ -std=c++17 -Wall -Wextra -pedantic (GCC 13+ via MSYS2/MinGW-w64 on Windows; GCC or clang++ on macOS/Linux — see ../../docs/TOOLCHAIN.md).
• Editor: any (VS Code + C/C++ extension recommended; debugger optional until Lab 4).
• Verify before starting:

  g++ --version

• Starter files for this lab live in starter_code/ next to this manual; they compile warning-free under the contract (see ../../../docs/LAB_AUDIT.md).

4. Relevant theory

decision tables, ladder order, switch-if translation, short-circuit guards — full treatment in the lecture notes; the lab applies it, the lecture explains it.

5. Pre-lab questions

Answer in your notebook BEFORE the session; the TA checks them at entry:

1. In a >= ladder, which threshold must be tested first, and why?
2. For which types does switch NOT work?
3. What does short-circuit evaluation protect in (b != 0 && a/b > 2)?

6. Instructor demonstration (15 min)

The instructor or TA demonstrates: if/else, ladders, switch, boolean operators. Watch for the workflow (how errors are read and fixed), not just the final code. The demo ends with the checkpoints you must hit in § 7.

7. Guided coding tasks

1. guided: elevator decision table to code
2. guided: grade ladder (correct order, then deliberately reversed)
3. independent: electricity tariff with slabs and a daily cap
4. independent: menu-driven shape calculator with switch

Checkpoint rule: show each guided result to the TA before moving on. TAs give guidance, not solutions (../../TEACHING_GUIDE.md § 5).

8. Independent programming exercises

Complete the tasks labeled independent in § 7 without step-by-step help. You may consult lecture notes and this manual — not a neighbor's screen. The TA records who completes what.

9. Debugging task

A tariff program with a reversed ladder — trace the wrong branch, fix

Use the five-step debug loop (reproduce, isolate, hypothesize, test, fix-and-verify) and record it in your debug log (../../labs/resources/debug_log_template.md) from Lab 4 onward. Identify the stage of each defect (compile, link, runtime, logic).

10. Test cases

Your program must pass at minimum:

• Boundary values (0, 1, maximum legal input).
• Normal cases from the task descriptions.
• At least one invalid input handled gracefully (from Lab 4 onward).

Record results in the test-evidence table (../../labs/resources/submission_template.md): input, expected, actual, verdict.

11. Expected learning outcomes

After this lab, verified by the checkpoints and your submission, you can reliably write decision tables before if-statements; order ladder branches so the most specific test runs first; translate if/else chains to switch and back; guard division and input ranges with early exits. This maps to the module's PF outcomes and feeds the next lab's prerequisites.

12. Submission requirements

Submit via the course LMS before the start of next week's lab:

1. Source file(s) named per the task list (snake_case).
2. Test-evidence table (completed template).
3. Debug log for the § 9 task (Lab 4 onward).
4. Pre-lab answers (photo or scan is fine).

Code must compile warning-free under the course contract — a warning costs the compile check (§ 13).

13. Assessment rubric (10 points)

Total 10, scaled to the 10 % course component. Labs 1–15 count the best 12 of 15 (drop-lowest); Lab 16 is graded as the project milestone with the same rubric plus the demo (see the instructor notes).