C Program for Simple DSC order Priority QUEUE Implementation using Structure

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C Program for Simple DSC order Priority QUEUE Implementation using Structure.
Source: Dr. G T Raju, Professor & Head, Dept. of CSE, RNSIT

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#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);
}

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