A summary of global variables and typedef

Want to use global variables , An error is reported when the following structure is used ：

///A.h
typedef struct student
{
	char *name;
	struct student*next;
}STUDENT;
///B.c
TOM=(STUDENT*)malloc(sizeof(STUDENT));

And then put typedef Remove all , Then change it to ：

struct student
{
	char *name;
	struct student*next;
}STUDENT;

TOM=(struct student*)malloc(sizeof(struct student));

It will be normal , do not know why .