Makefile.ver1_explained

# define C compiler & flags
CC = gcc
CFLAGS = -Wall
# just like #define in C, here:
#    CC becomes a symbolic name, and is equivalent to "gcc"
#    CFLAGS is equivalent to "-Wall"
# use CFLAGS = -g -Wall
# if you want to run debugging tools such as valgrind and gdb
# but note that the flag "-g" makes the excutable code slower.

# define libraries to be linked (for example -lm)
LIB = 
#   LIB is equivalent to "" (empty), 
#   if we want to compile with "-lm" we should write:
#   LIB = -lm

HDR = factorial.h
SRC = main.c factorial.c
# HDR, SRC are symbolic names,
# each of them is a string containing several file names
#    HDR contains all .h files of the project
#    SRC contains all .c files of the project


# OBJ is the same as SRC, just sustitute ".c" with ".o"
OBJ     = $(SRC:.c=.o)
# so, OBJ becomes "main.o factorial.o"
# recall that "factorial.o" stands for the object file
# translated by "gcc" from "factorial.c", ie. it is the product of command:
#     gcc -c factorial.c

# the executable name
EXE = factorial

$(EXE): $(HDR) $(OBJ) Makefile
	$(CC) $(CFLAGS) -o $(EXE) $(OBJ) $(LIB)
# so, factorial (ie EXE) depends on 
#   main.o factorial.o
# and is associated with command:
#   gcc -Wall -o main.o factorial.o


clean: 
	rm -f $(OBJ) $(EXE)
# The target "clean" helps to remove all files "make" created, include
#     all `.o` files ( which are in OBJ) 
#     end the file factorial (whic is EXE). 
# The purpose running "make clean" is:
#   - for you to be able to recompile the project 
#     (for example, after copying the project to a different computers)
#   - to clean the non-essential files so that you can economically
#     copy the whole project to an archive.
 

$(OBJ): $(HDR)
# The last lines just state the dependencies for the objects .o files
# It means that when one of the file in the list HDR changed,
# "make" must rebuild the .o files (ie. recompile them).