Implements circular queue as an array.

C: Program that implements circular queue as an array.

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

#define MAX 10

void addq ( int *, int, int *, int * ) ;
int delq ( int *, int *, int * ) ;
void display ( int * ) ;

void main( )
{
    int arr[MAX] ;
    int i, front, rear ;

    clrscr( ) ;

    /* initialise data member */
    front = rear = -1 ;
    for ( i = 0 ; i < MAX ; i++ )
        arr[i] = 0 ;

    addq ( arr, 14, &front, &rear ) ;
    addq ( arr, 22, &front, &rear ) ;
    addq ( arr, 13, &front, &rear ) ;
    addq ( arr, -6, &front, &rear ) ;
    addq ( arr, 25, &front, &rear ) ;

    printf ( "\nElements in the circular queue: " ) ;
    display ( arr ) ;

    i = delq ( arr, &front, &rear ) ;
    printf ( "Item deleted: %d", i ) ;

    i = delq ( arr, &front, &rear ) ;
    printf ( "\nItem deleted: %d", i ) ;

    printf ( "\nElements in the circular queue after deletion: " ) ;
    display ( arr ) ;

    addq ( arr, 21, &front, &rear ) ;
    addq ( arr, 17, &front, &rear ) ;
    addq ( arr, 18, &front, &rear ) ;
    addq ( arr, 9, &front, &rear ) ;
    addq ( arr, 20, &front, &rear ) ;

    printf ( "Elements in the circular queue after addition: " ) ;
    display ( arr ) ;

    addq ( arr, 32, &front, &rear ) ;

    printf ( "Elements in the circular queue after addition: " ) ;
    display ( arr ) ;

    getch( ) ;
}

/* adds an element to the queue */
void addq ( int *arr, int item, int *pfront, int *prear )
{
    if ( ( *prear == MAX - 1 && *pfront == 0 ) || (  *prear + 1 == *pfront ) )
    {
        printf ( "\nQueue is full." ) ;
        return ;
    }

    if ( *prear == MAX - 1 )
        *prear = 0 ;
    else
        ( *prear )++ ;

    arr[*prear] = item ;

    if ( *pfront == -1 )
        *pfront = 0 ;
}

/* removes an element from the queue */
int delq ( int *arr, int *pfront, int *prear )
{
    int data ;

    if ( *pfront == -1 )
    {
        printf ( "\nQueue is empty." ) ;
        return NULL ;
    }

    data = arr[*pfront] ;
    arr[*pfront] = 0 ;

    if ( *pfront == *prear )
    {
        *pfront = -1 ;
        *prear = -1 ;
    }
    else
    {
        if ( *pfront == MAX - 1 )
            *pfront = 0 ;
        else
            ( *pfront )++ ;
    }
    return data ;
}

/* displays element in a queue */
void display ( int * arr )
{
    int i ;
    printf ( "\n" ) ;
    for ( i = 0 ; i < MAX ; i++ )
        printf ( "%d\t", arr[i] ) ;
    printf ( "\n" ) ;
}