C Program for Simple DSC order Priority QUEUE Implementation using Structure

#define SIZE 5            /* Size of Queue */
int f=0,r=-1;       /* Global declarations */
typedef struct PRQ
{
int ele;
int pr;
}PriorityQ;
 
PriorityQ PQ[SIZE];
 
PQinsert(int elem, int pre)
{
int i;       /* Function for Insert operation */
if( Qfull()) printf("\n\n Overflow!!!!\n\n");
else
{
i=r;
++r;
while(PQ[i].pr <= pre && i >= 0) /* Find location for new elem */
{
PQ[i+1]=PQ[i];
i--;
}
PQ[i+1].ele=elem;
PQ[i+1].pr=pre;
}
}
 
PriorityQ PQdelete()
{                      /* Function for Delete operation */
PriorityQ p;
if(Qempty()){ printf("\n\nUnderflow!!!!\n\n");
p.ele=-1;p.pr=-1;
return(p); }
else
{
p=PQ[f];
f=f+1;
return(p);
}
}
 
int Qfull()
{                     /* Function to Check Queue Full */
if(r==SIZE-1) return 1;
return 0;
}
 
int Qempty()
{                    /* Function to Check Queue Empty */
if(f > r) return 1;
return 0;
}
 
display()
{                  /* Function to display status of Queue */
int i;
if(Qempty()) printf(" \n Empty Queue\n");
else
{
printf("Front->");
for(i=f;i<=r;i++)
printf("[%d,%d] ",PQ[i].ele,PQ[i].pr);
printf("<-Rear");
}
}
 
main()
{                         /* Main Program */
int opn;
PriorityQ p;
do
{
clrscr();
printf("\n ### Priority Queue Operations(DSC order) ### \n\n");
printf("\n Press 1-Insert, 2-Delete,3-Display,4-Exit\n");
printf("\n Your option ? ");
scanf("%d",&opn);
switch(opn)
{
case 1: printf("\n\nRead the element and its Priority?");
scanf("%d%d",&p.ele,&p.pr);
PQinsert(p.ele,p.pr); break;
case 2: p=PQdelete();
if( p.ele != -1)
printf("\n\nDeleted Element is %d \n",p.ele);
break;
case 3: printf("\n\nStatus of Queue\n\n");
display(); break;
case 4: printf("\n\n Terminating \n\n"); break;
default: printf("\n\nInvalid Option !!! Try Again !! \n\n");
break;
}
printf("\n\n\n\n  Press a Key to Continue . . . ");
getch();
}while(opn != 4);
}