C question. Declaring data on new nod to NULL, possible?

[freedon]

First I'll explain what I need to do. I have to use pointers with Dinamic Memory.

This is schoolwork. The purpose is have a code of the registration of the clients on a hotel.

(the code will be on the bottom)

First, ask how many rooms does the hotel have. Then using a for loop, create new nods (In spanish we call it nodos, I guess NOD is the translation to english). Inside the loop, create new nod and fill it with data [the room equals to the same number as t (the variable I use to control the loop). But the other data, name, address, sex, phone number, etc I want to put NULL. At first I tried filling it with just a string of data {"----"}, didn't work, so later I declared a variable that had {"----"} and I equalled name, address, etc to that variable, didn't even compile. So I'm stuck there, I'm almost done with the rest of the code.

typedef struct nodo
{
int cuarto;            //room
char nombre[30];         //name
char dir[30];           //address
char tel[8];           //phone number
char sexo;             //sex
struct nodo *enlace;                 //enlace is used to connect nods


}lista;


lista *ptr=NULL;
lista *p1,*p2,*p3,*prin,*nuevo;

int opmain, num=0,total ,t=0 ,opcuarto ,opreportecliente ,opreporte1 ,opregistro ,opmain2;

char sex, vacio[4] = {"----"},vacio2[1] = {'-'};



MAIN CODE
void main(void)
{
The main code does work, too long to post :p 
call function crearcuartos (create rooms)

}



void crearcuartos()
{
if(total!=0||ptr!=NULL)
	printf("\nRooms have already been defined");
else
{
	printf("\nHow many rooms in the hotel: ");
	scanf("%d",&num);

	for(t=0;t<num;t++)
	{

	nuevo=(lista*)malloc(sizeof(lista));

	flushall();
	nuevo->cuarto=(num-t);


	flushall();
	nuevo->nombre[t]=vacio2[t];
	
	flushall();
	nuevo->dir[t]=vacio[t];
	
	flushall();
	nuevo->tel=NULL;
	
	flushall();
	nuevo->sexo='-';
	

	
	if(ptr==NULL)          //if nod is the first created
	{
	   nuevo->enlace=NULL;  //new nod of connect is equal to NULL
	   ptr=nuevo;         //ptr (main pointer) equals new nod position
	}
	else
	{
		nuevo->enlace=ptr;   //new nod connects to ptr
		ptr=nuevo;           //ptr equals new position

	}
	


}

}		//**end function 'create rooms'

As you can see in this part
flushall();
nuevo->nombre[t]=vacio2[t];

flushall();
nuevo->dir[t]=vacio[t];

flushall();
nuevo->tel=NULL;


I tried 3 different ways, equal to the value of vacio2, vacio and NULL, neither work. NULL doesn't even compile, I get a "Lvalue requiered"


flushall();
nuevo->sexo='-';



this one does work

Hope someone can help me before I go crazy