Problem in compiling root 6

Hello,
I am compiling root 6 and everything went fine until I got this error,
input_line_3input_line_3::11::1010:: fatal errorfatal error: : ‘assert.h’‘assert.h’ filefile notnot foundfound

#include <assert.h>#include <assert.h>

     ^         ^

Error: Error: Error loading the default header files.
Error loading the default header files.
make: *** [core/metautils/src/G__std__vector.cxx] Error 1
make: *** Waiting for unfinished jobs…
make: *** [core/base/src/G__Core.cxx] Error 1

the problem is solved by
xcode-select --install