Chapter 2 Exercises

Work through these after reading Chapter 2. Try each one yourself before revealing the solution — you learn far more from an honest attempt than from reading a finished answer.

When you open a solution it appears blurred — click it once more to reveal it, so you do not see the answer by accident.

These exercises are done in a real project and terminal — a CMakeLists.txt you write and a sequence of git commands you run. There is nothing to "run on Compiler Explorer"; the point is to do them for real on your own machine. (PlatformIO has no paper exercise — it needs a real board, so its practice belongs in the lab with hardware in hand.)

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1. A project with two programs

Practises: CMake

You want to keep two of your Chapter 1 solutions — ex1.cpp and ex2.cpp — in a single project, each runnable on its own. Write a CMakeLists.txt that builds both as separate executables, uses C++20, and turns compiler warnings on for each.

Show solution

cmake_minimum_required(VERSION 3.16)
project(chapter1_solutions)

set(CMAKE_CXX_STANDARD 20)
set(CMAKE_CXX_STANDARD_REQUIRED ON)

if(MSVC)
    add_compile_options(/W4)
else()
    add_compile_options(-Wall -Wextra)
endif()

add_executable(ex1 ex1.cpp)
add_executable(ex2 ex2.cpp)

One add_executable per program gives you two entries in the run-configuration dropdown next to the green ▶ button — exactly the setup the Chapter 1 exercises suggested. CMAKE_CXX_STANDARD is set once near the top and applies to every target below it. The warning flags go behind an if(MSVC) branch, exactly as the chapter shows: hard-coding -Wall -Wextra alone would break the moment someone built this with Visual Studio, which spells the flag /W4. Putting the flags in add_compile_options before the targets applies them to both executables at once, so there is no per-target line to repeat.

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2. Save your work with git

Practises: Version Control & Git

You have just created a new project folder containing a CMakeLists.txt and a main.cpp. Using git, (1) turn the folder into a repository, (2) save both files in a first commit with a sensible message, and then (3) start a branch called experiment to try a change without disturbing main. Write the commands in order.

Hint: a quick git status between steps is always a good way to check what git thinks is going on.

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git init                                  # turn the folder into a repo
git status                                # see what is untracked

git add CMakeLists.txt main.cpp           # stage both files
git commit -m "Initial project: builds Hello World"

git switch -c experiment                  # create + move onto a new branch

git add only stages the files — it marks them for the next snapshot. git commit is what actually records the snapshot, and its message says what this state is. git switch -c experiment creates the branch and moves you onto it in one step; anything you commit now lands on experiment, leaving main untouched until you choose to merge.

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3. Share code between two programs with a library

Practises: CMake

Both of your programs need the same helper — say a motor.cpp / motor.hpp pair with a motorRpm() function. Rather than list motor.cpp in both add_executable lines (compiling it twice), put it in a library and link that library into each program. Write a CMakeLists.txt that builds motor.cpp as a library and links it into two executables, app and bench.

Hint: add_library defines the library target; target_link_libraries(<exe> PRIVATE <lib>) links it into an executable. A program that links the library also sees its headers.

Show solution

cmake_minimum_required(VERSION 3.16)
project(motor_tools)

set(CMAKE_CXX_STANDARD 20)
set(CMAKE_CXX_STANDARD_REQUIRED ON)

add_library(motor motor.cpp)          # shared code, compiled once

add_executable(app app.cpp)
target_link_libraries(app PRIVATE motor)

add_executable(bench bench.cpp)
target_link_libraries(bench PRIVATE motor)

motor.cpp is now compiled a single time into the motor library; each target_link_libraries line pulls that compiled code (and motor's headers) into one executable. If the helper had its own include/ folder you would add target_include_directories(motor PUBLIC include) so both programs pick the headers up automatically — PUBLIC because anything linking motor should also see them. This is the pattern the chapter's Building libraries section describes, and it is how a project with tests keeps its production code in one place.