c - Make: *** [] Error 1 -

i've made makefile , trying test getting error in make:

austins-macbook:work4 staffmember$ make new rm -f main.o heap.o heap gcc -wall -o2   -c -o main.o main.c gcc -wall -o2   -c -o heap.o heap.c heap.c: in function ‘createheap’: heap.c:6: warning: implicit declaration of function ‘malloc’ heap.c:6: warning: incompatible implicit declaration of built-in function ‘malloc’ heap.c:8: warning: implicit declaration of function ‘exit’ heap.c:8: warning: incompatible implicit declaration of built-in function ‘exit’ gcc -wall -o2 -o heap main.o heap.o austins-macbook:work4 staffmember$ make test ./heap make: *** [test] error 1 

i thought getting make * error 1 meant 1 of components did not compile properly, there weren't error messages when compiled it. how find out problem is?

./heap returned non-zero exit code, make interpreting error. make sure doing return 0; @ end of main.