C Program for Circular QUEUE Operations – using Array

#define SIZE 5            /* Size of Circular Queue */
int CQ[SIZE],f=-1,r=-1;       /* Global declarations */
 
CQinsert(int elem)
{                       /* Function for Insert operation */
    if( CQfull()) printf("\n\n Overflow!!!!\n\n");
    else
    {
        if(f==-1)f=0;
        r=(r+1) % SIZE;
        CQ[r]=elem;
    }
}
int CQdelete()
{                      /* Function for Delete operation */
    int elem;
    if(CQempty()){ printf("\n\nUnderflow!!!!\n\n");
    return(-1); }
    else
    {
        elem=CQ[f];
        if(f==r){ f=-1; r=-1;} /* Q has only one element ? */
        else
            f=(f+1) % SIZE;
        return(elem);
    }
}
int  CQfull()
{                     /* Function to Check Circular Queue Full */
    if( (f==r+1) || (f == 0 && r== SIZE-1)) return 1;
    return 0;
}
 
int CQempty()
{                    /* Function to Check Circular Queue Empty */
    if(f== -1) return 1;
    return 0;
}
 
display()
{        /* Function to display status of Circular Queue */
    int i;
    if(CQempty()) printf(" \n Empty Queue\n");
    else
    {
        printf("Front[%d]->",f);
        for(i=f;i!=r;i=(i+1)%SIZE)
            printf("%d ",CQ[i]);
        printf("%d ",CQ[i]);
        printf("<-[%d]Rear",r);
    }
}
 
main()
{                         /* Main Program */
    int opn,elem;
    do
    {
        clrscr();
        printf("\n ### Circular Queue Operations ### \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 to be Inserted ?");
            scanf("%d",&elem);
            CQinsert(elem); break;
        case 2: elem=CQdelete();
            if( elem != -1)
                printf("\n\nDeleted Element is %d \n",elem);
            break;
        case 3: printf("\n\nStatus of Circular 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);
}