Lab 13 · Pointers

Module 13 · Lectures L25–L26 · Week 13 · 120 minutes · guided/independent 40/60

Prerequisites: completion of Labs 1–12 (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:

• Apply & and * correctly and explain each
• Walk arrays with pointers and pointer arithmetic
• Use nullptr and check before dereference
• Contrast pointers with references

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

&/*, pointer arithmetic, null checks, reference vs pointer — 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. What does &x give, and what type is it?
2. What does p++ advance by for an int*?
3. Why is dereferencing nullptr undefined rather than 'an error message'?

6. Instructor demonstration (15 min)

The instructor or TA demonstrates: Addresses, dereference, pointer safety. 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: address/dereference exploration on int and double
2. guided: array walk with a pointer (print via *p)
3. independent: safe-pointer toolkit (null-guarded print, swap via pointers)
4. independent: pointer-based min/max finder with span arithmetic

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

Three pointer hazards clinic (uninitialized, null, dangling) — guarded fixes

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 apply & and * correctly and explain each; walk arrays with pointers and pointer arithmetic; use nullptr and check before dereference; contrast pointers with references. 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).