you don't initialize variables in header files becuse the variables don't exist. You have to declare variables in *.c or *.cpp files. You can, however, use the extern keyword with variable in header files, but again they can not be initialized there.
// myheader.h file
extern int myint;
Then in one, and only one, *.cpp file you declare the same variable but without extern keyword. You can also initialize it then.
int myint = 0;