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" ) ;
}