c++ undefined reference to `main' while compiling - c++

Question

After try to use this attached makefile the error that appears is :
(.text+0x20): undefined reference to `main'
collect2: error: ld returned 1 exit status
make: *** [Ass1F] Error 1
the makefile is :
all: Ass1F
Ass1F: bin/main.o bin/x.o bin/y.o bin/z.o bin/w.o
g++ -o bin/main.o bin/x.o bin/y.o bin/z.o bin/w.o
#echo 'Finished building target: Ass1F'
#echo ' '
bin/x.o: src/x.cpp
g++ -g -Wall -Weffc++ -c -Linclude -o bin/x.o src/x.cpp
bin/y.o: src/y.cpp
g++ -g -Wall -Weffc++ -c -Linclude -o bin/y.o src/y.cpp
bin/z.o: src/z.cpp
g++ -g -Wall -Weffc++ -c -Linclude -o bin/z.o src/z.cpp
bin/w.o: src/w.cpp
g++ -g -Wall -Weffc++ -c -Linclude -o bin/w.o src/w.cpp
bin/main.o: src/main.cpp
g++ -g -Wall -Weffc++ -c -Linclude -o bin/main.o src/main.cpp
clean:
rm -f bin/*
what should I do with this problem?
the reason is the makefile or something in the code?
just to let you know we used eclipse to write the code and everything work perfectly- no any bugs.
thanks

Answer 1

Line g++ -o bin/main.o bin/x.o bin/y.o bin/z.o bin/w.o tries to create executable named bin/main.o, overwriting its previous contents.
It should be e.g. g++ -o Ass1F bin/main.o bin/x.o bin/y.o bin/z.o bin/w.o

Answer 2

Your makefile recipe for Ass1F is incorrect, it doesn't specify the output file, os make uses bin/main.o as the output file instead of one of the input files.
You can simplify the makefile by using pattern rules (i.e. with wildcards) and using pre-defined variables such as $# (the name of the target) and $^ (the list of prerequisites) and CXX (the C++ compiler):
CXXFLAGS = -g -Wall -Weffc++
CPPFLAGS =
LDFLAGS =
LDLIBS =
all: Ass1F
Ass1F: bin/main.o bin/x.o bin/y.o bin/z.o bin/w.o
$(CXX) $(LDFLAGS) -o $# $^ $(LDLIBS)
#echo 'Finished building target: Ass1F'
#echo ' '
bin/%.o: src/%.cpp
$(CXX) $(CPPFLAGS) $(CXXFLAGS) -c -o $# $^
clean:
rm -f bin/*