Implements a priority queue using an array.

C: Program that implements a priority queue using an array.

#include <stdio.h>
#include <conio.h>

#define MAX 5

struct data
{
    char job[MAX] ;
    int prno ;
    int ord ;
} ;

struct pque
{
    struct data d[MAX] ;
    int front ;
    int rear ;
} ;

void initpque ( struct pque * ) ;
void add ( struct pque *, struct data ) ;
struct data delete ( struct pque * ) ;

void main( )
{
    struct pque q ;
    struct data dt, temp ;
    int i, j = 0 ;

    clrscr( ) ;

    initpque ( &q ) ;

    printf ( "Enter Job description (max 4 chars) and its priority\n" ) ;
    printf ( "Lower the priority number, higher the priority\n" ) ;
    printf ( "Job     Priority\n" ) ;

    for ( i = 0 ; i < MAX ; i++ )
    {
        scanf ( "%s %d", &dt.job, &dt.prno ) ;
        dt.ord = j++ ;
        add ( &q, dt ) ;
    }
    printf ( "\n" ) ;

    printf ( "Process jobs prioritywise\n" ) ;
    printf ( "Job\tPriority\n" ) ;

    for ( i = 0 ; i < MAX ; i++ )
    {
        temp  = delete ( &q ) ;
        printf ( "%s\t%d\n", temp.job, temp.prno ) ;
    }
    printf ( "\n" ) ;

    getch( ) ;
}

/* initialises data members */
void initpque ( struct pque *pq )
{
    int i ;

    pq -> front = pq -> rear = -1 ;
    for ( i = 0 ; i < MAX ; i++ )
    {
        strcpy ( pq -> d[i].job, '\0' ) ;
        pq -> d[i].prno = pq -> d[i].ord = 0 ;
    }
}

/* adds item to the priority queue */
void add ( struct pque *pq, struct data dt )
{
    struct data temp ;
    int i, j ;

    if ( pq -> rear == MAX - 1 )
    {
        printf ( "\nQueue is full." ) ;
        return ;
    }

    pq -> rear++ ;
    pq -> d[pq -> rear] = dt ;

    if ( pq -> front == -1 )
        pq -> front = 0 ;

    for ( i = pq -> front ; i <= pq -> rear ; i++ )
    {
        for ( j = i + 1 ; j <= pq -> rear ; j++ )
        {
            if ( pq -> d[i].prno > pq -> d[j].prno )
            {
                temp = pq -> d[i] ;
                pq -> d[i] = pq -> d[j] ;
                pq -> d[j] = temp ;
            }
            else
            {
                if ( pq -> d[i].prno == pq -> d[j].prno )
                {
                    if ( pq -> d[i].ord > pq -> d[j].ord )
                    {
                        temp = pq -> d[i] ;
                        pq -> d[i] = pq -> d[j] ;
                        pq -> d[j] = temp ;
                    }
                }
            }
        }
    }
}

/* removes item from priority queue */
struct data  delete ( struct pque *pq )
{
    struct data  t ;
    strcpy ( t.job, "" ) ;
    t.prno = 0 ;
    t.ord = 0 ;

    if ( pq -> front == -1 )
    {
        printf ( "\nQueue is Empty.\n" ) ;
        return t ;
    }

    t = pq -> d[pq -> front] ;
    pq -> d[pq -> front] = t ;
    if ( pq -> front == pq -> rear )
         pq -> front = pq -> rear = -1 ;
    else
         pq -> front++ ;

    return  t ;
}