spreading source across folders

[rowdy]

i am having trouble with getting source files to compile when they include headers in different folders.

eg.

src/folderA/constants.h:

#define constant1 51

src/folderB/program.c

#include "constants.h"
#include <iostream>
int main () {
	cout << constant1;
	return 0;
}

src/makefile:

program: program.o
	$(CC) program.o -o program
program.o: src/folderB/program.c
	$(CC) -c src/folderB/program.c -o program.o

This won't compile since program.c doesn't know where constants.h is,