Makefile doesn't find source files - makefile

Question

I have tried to make a makefile. I have the following folder structure.
Source
- include
- My headerfiles
- objects
- The object files
- src
- My source files
My problem is that the source files in the src directory isn't found.
My make file looks as the following.
# gcc for C
# g++ for c++
CC = gcc
#compiler flags
# -g adds debugging information to the executebells
# -Wall
CFLAGS = -g -Wall
#target
TARGET = gabe_the_dog_server
#directory for the object files
OBJDIR = ./objects
SRCDIR = ./src
default: $(TARGET)
all: default
HEADERS = $(wildcard include/*.h)
OBJECTS := $(SOURCES:$(SRCDIR)/%.c=$(OBJDIR)/%.o)
$(OBJDIR)/%.o: $(SRCDIR)/%.c $(HEADERS)
$(CC) $(CFLAGS) -c $< -o $#
$(TARGET): $(OBJECTS)
$(CC) $(OBJECTS) $(CFLAGS) $(LIBS) -o $(OBJDIR)/$#
$(OBJECTS): $(OBJDIR)/%.o : $(SRCDIR)/%.c
$(CC) $(CFLAGS) -c $< -o $#
clean:
-rm -f *.o
-rm -f $(TARGET)

Answer 1

Here:
OBJECTS := $(SOURCES:$(SRCDIR)/%.c=$(OBJDIR)/%.o)
You use the variable SOURCES, but you never define it. You need one more line:
SOURCES = $(wildcard $(SRCDIR)/*.c)
OBJECTS := $(SOURCES:$(SRCDIR)/%.c=$(OBJDIR)/%.o)

Answer 2

Instead of using the path to your source files, it's recommended that you put this path in the special variable named VPATH. Then you just mention your source file, like this:
OBJDIR = ./obj
SRCDIR = ./src
VPATH = $(SRCDIR)
OBJECTS = $(addprefix $(OBJDIR)/, foo.o bar.o)
all: $(OBJECTS)
$(OBJDIR)/%.o: %.c
$(cc) ...
GNU make will look in the folders present in VPATH for the files that are prerequisites of a target. Note that this could be a problem if you have multiple folders where you can find multiple times the same file name.
See GNU make VPATH manual. If you need additional examples of VPATH good practices, see this link as well: Mad Scientist: How not to use VPATH