Building multiple executables with similar rules

You can actually do this with a few lines of GNU Make.

Below are two makefiles that allow building and cleaning from all_lessons directory and individual project directories. It assumes that all C++ sources in that directory comprise an executable file which gets named after its directory. When building and cleaning from the top level source directory (all_lessons) it builds and cleans all the projects. When building and cleaning from a project’s directory it only builds and cleans the project’s binaries.

These makefiles also automatically generate dependencies and are fully parallelizable (make -j friendly).

For the following example I used the same source file structure as you have:

$ find all_lessons
all_lessons
all_lessons/even_or_odd
all_lessons/even_or_odd/main.cpp
all_lessons/Makefile
all_lessons/helloworld
all_lessons/helloworld/lesson.cpp
all_lessons/helloworld/main.cpp
all_lessons/project.mk
all_lessons/calculator
all_lessons/calculator/lesson.cpp
all_lessons/calculator/user_created_add.cpp
all_lessons/calculator/main.cpp

To be able to build from individial project directories project.mk must be symlinked as project/Makefile first

[all_lessons]$ cd all_lessons/calculator/
[calculator]$ ln -s ../project.mk Makefile
[helloworld]$ cd ../helloworld/
[helloworld]$ ln -s ../project.mk Makefile
[even_or_odd]$ cd ../even_or_odd/
[even_or_odd]$ ln -s ../project.mk Makefile

Let’s build one project:

[even_or_odd]$ make
make -C .. project_dirs=even_or_odd all
make[1]: Entering directory `/home/max/src/all_lessons'
g++ -c -o even_or_odd/main.o -Wall -Wextra   -MD -MP -MF even_or_odd/main.d even_or_odd/main.cpp
g++ -o even_or_odd/even_or_odd even_or_odd/main.o  
make[1]: Leaving directory `/home/max/src/all_lessons'
[even_or_odd]$ ./even_or_odd
hello, even_or_odd

Now build all projects:

[even_or_odd]$ cd ..
[all_lessons]$ make
g++ -c -o calculator/lesson.o -Wall -Wextra   -MD -MP -MF calculator/lesson.d calculator/lesson.cpp
g++ -c -o calculator/user_created_add.o -Wall -Wextra   -MD -MP -MF calculator/user_created_add.d calculator/user_created_add.cpp
g++ -c -o calculator/main.o -Wall -Wextra   -MD -MP -MF calculator/main.d calculator/main.cpp
g++ -o calculator/calculator calculator/lesson.o calculator/user_created_add.o calculator/main.o  
g++ -c -o helloworld/lesson.o -Wall -Wextra   -MD -MP -MF helloworld/lesson.d helloworld/lesson.cpp
g++ -c -o helloworld/main.o -Wall -Wextra   -MD -MP -MF helloworld/main.d helloworld/main.cpp
g++ -o helloworld/helloworld helloworld/lesson.o helloworld/main.o  
[all_lessons]$ calculator/calculator 
hello, calculator
[all_lessons]$ helloworld/helloworld
hello, world

Clean one project:

[all_lessons]$ cd helloworld/
[helloworld]$ make clean
make -C .. project_dirs=helloworld clean
make[1]: Entering directory `/home/max/src/all_lessons'
rm -f helloworld/lesson.o helloworld/main.o helloworld/main.d helloworld/lesson.d helloworld/helloworld
make[1]: Leaving directory `/home/max/src/all_lessons'

Clean all projects:

[helloworld]$ cd ..
[all_lessons]$ make clean
rm -f calculator/lesson.o calculator/user_created_add.o calculator/main.o even_or_odd/main.o helloworld/lesson.o helloworld/main.o calculator/user_created_add.d calculator/main.d calculator/lesson.d even_or_odd/main.d  calculator/calculator even_or_odd/even_or_odd helloworld/helloworld

The makefiles:

[all_lessons]$ cat project.mk 
all :
% : forward_ # build any target by forwarding to the main makefile
    $(MAKE) -C .. project_dirs=$(notdir ${CURDIR}) $@
.PHONY : forward_

[all_lessons]$ cat Makefile 
# one directory per project, one executable per directory
project_dirs := $(shell find * -maxdepth 0 -type d )

# executables are named after its directory and go into the same directory
exes := $(foreach dir,${project_dirs},${dir}/${dir})

all : ${exes}

#  the rules

.SECONDEXPANSION:

objects = $(patsubst %.cpp,%.o,$(wildcard $(dir ${1})*.cpp))

# link
${exes} : % : $$(call objects,$$*) Makefile
    g++ -o $@ $(filter-out Makefile,$^) ${LDFLAGS} ${LDLIBS}

# compile .o and generate dependencies
%.o : %.cpp Makefile
    g++ -c -o $@ -Wall -Wextra ${CPPFLAGS} ${CXXFLAGS} -MD -MP -MF ${@:.o=.d} $<

.PHONY: clean

clean :
    rm -f $(foreach exe,${exes},$(call objects,${exe})) $(foreach dir,${project_dirs},$(wildcard ${dir}/*.d)) ${exes}

# include auto-generated dependency files
-include $(foreach dir,${project_dirs},$(wildcard ${dir}/*.d))