Circular queue of strings using an array

/* A program for circular queue of strings using an array */
#include<stdlib.h>
#include<stdio.h>
#include<string.h>
#define MAX 10

typedef struct Q
{
int R,F;
char *data[MAX];
}Q;

void initialise(Q *P);
int empty(Q *P);
int full(Q *P);
void enqueue(Q *P,char *x);
char * dequeue(Q *P);
void print(Q *P);
int main()
{ Q q;
       int op;
       char x[40],*y;
     initialise(&q);
        do{
printf("\n\n1)Insert\n2)Delete\n3)Print\n4)Quit");
printf("\nEnter Your Choice:");
scanf("%d",&op);
switch(op)
{ case 1: printf("\n Enter string:");

   fflush(stdin);
   scanf("%s",x);
   if(!full(&q))
{
y=(char*)malloc(strlen(x)+1);
strcpy(y,x);
enqueue(&q,y);
}
   else
printf("\nQueue is full !!!!");
 

  break;
  case 2:if(!empty(&q))
   {
y=dequeue(&q);
printf("\nDeleted Data=%s",y);
   }
  else
printf("\nQueue is empty !!!!");
  break;
  case 3: print(&q);break;
}
      }while(op!=4);
}

void initialise(Q *P)
{
int i;
for(i=0;i<MAX;i++)
P->data[i]=NULL;
P->R=-1;
P->F=-1;
}

int empty(Q *P)
{
if(P->R==-1)
return(1);
return(0);
}

int full(Q *P)
{
if((P->R+1)%MAX==P->F)
return(1);
return(0);
}

void enqueue(Q *P,char *x)
{
if(P->R==-1)
{
P->R=P->F=0;
if(P->data[P->R]!=NULL)
free(P->data[P->R]);
P->data[P->R]=x;
}
else
{
P->R=(P->R+1)%MAX;
if(P->data[P->R]!=NULL)
free(P->data[P->R]);
P->data[P->R]=x;
}
}

char * dequeue(Q *P)
{
char *x;
x=P->data[P->F];
if(P->R==P->F)
{
P->R=-1;
P->F=-1;
}
else
P->F=(P->F+1)%MAX;
return(x);
}

void print(Q *P)
{
int i;
if(!empty(P))
{
printf("\n");
for(i=P->F;i!=P->R;i=(i+1)%MAX)
printf("%s\t",P->data[i]);
}
       printf("%s\t",P->data[i]);
}