#define HELLO "Hello"

#include "hello.h"

char *
hello() 
{
  return HELLO;
}

#define WORLD "world"

#include "world.h"

char *
world() 
{
  return WORLD;
}

#include <stdio.h>
#include "hello.h"
#include "world.h"

/* Prototypes. */
char *hello();
char *world();

void
printhelloworld()
{
    printf("%s, %s!\n", hello(), world());
    printf("I just said %s to the %s.\n", HELLO, WORLD);
    return;
}

/* Prototypes. */
void printhelloworld();

int
main(int argc, char *argv[]) 
{
    printhelloworld();
    return 0;
}

$ gcc -MM *.c
hello.o: hello.c hello.h
main.o: main.c
printhelloworld.o: printhelloworld.c hello.h world.h
world.o: world.c world.h

main.o: main.c
printhelloworld.o: printhelloworld.c hello.h world.h
hello.o: hello.c hello.h
world.o: world.c world.h

main.o: main.c
        cc -c main.c # TAB before command!

printhelloworld.o: printhelloworld.c hello.h world.h
        cc -c printhelloworld.c # TAB before command!

hello.o: hello.c hello.h
        cc -c hello.c # TAB before command!

world.o: world.c world.h
        cc -c world.c # TAB before command!

# The executable 'helloworld' depends on all object files
helloworld: main.o printhelloworld.o hello.o world.o
        cc -o helloworld main.o printhelloworld.o hello.o world.o # TAB before command!

main.o: main.c
        cc -c main.c # TAB before command!

printhelloworld.o: printhelloworld.c hello.h world.h
        cc -c printhelloworld.c # TAB before command!

hello.o: hello.c hello.h
        cc -c hello.c # TAB before command!

world.o: world.c world.h
        cc -c world.c # TAB before command!

# Remove object files, executables (UNIX/Windows), Emacs backup files, and core files
.PHONY : clean
clean:
        rm -rf  *.o helloworld helloworld.exe *~ *.core core # TAB before command!

OBJECTS = main.o printhelloworld.o hello.o world.o

OBJECTS = main.o printhelloworld.o hello.o world.o

# The executable 'helloworld' depends on all object files listed in $(OBJECTS)
helloworld: $(OBJECTS)
        cc -o helloworld $(OBJECTS) # TAB before command!

main.o: main.c
        cc -c main.c # TAB before command!

printhelloworld.o: printhelloworld.c hello.h world.h
        cc -c printhelloworld.c # TAB before command!

hello.o: hello.c hello.h
        cc -c hello.c # TAB before command!

world.o: world.c world.h
        cc -c world.c # TAB before command!

# Remove object files, executables (UNIX/Windows), Emacs backup files, and core files
.PHONY : clean
clean:
        rm -rf $(OBJECTS) helloworld helloworld.exe *~ *.core core # TAB before command!