Program that implements deque using an array.

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

#define MAX 10

void addqatbeg ( int *, int, int *, int * ) ;
void addqatend ( int *, int, int *, int * ) ;
int delqatbeg ( int *, int *, int * ) ;
int delqatend ( int *, int *, int * ) ;
void display ( int * ) ;
int count ( int * ) ;

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

clrscr( ) ;

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

addqatend ( arr, 17, &front, &rear ) ;
addqatbeg ( arr, 10, &front, &rear ) ;
addqatend ( arr, 8, &front, &rear ) ;
addqatbeg ( arr, -9, &front, &rear ) ;
addqatend ( arr, 13, &front, &rear ) ;
addqatbeg ( arr, 28, &front, &rear ) ;
addqatend ( arr, 14, &front, &rear ) ;
addqatbeg ( arr, 5, &front, &rear ) ;
addqatend ( arr, 25, &front, &rear ) ;
addqatbeg ( arr, 6, &front, &rear ) ;
addqatend ( arr, 21, &front, &rear ) ;
addqatbeg ( arr, 11, &front, &rear ) ;

printf ( "\nElements in a deque: " ) ;
display ( arr ) ;

n = count ( arr ) ;
printf ( "\nTotal number of elements in deque: %d", n ) ;

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

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

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

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

printf ( "\nElements in a deque after deletion: " ) ;
display ( arr ) ;

addqatend ( arr, 16, &front, &rear ) ;
addqatend ( arr, 7, &front, &rear ) ;

printf ( "\nElements in a deque after addition: " ) ;
display ( arr ) ;

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

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

printf ( "\nElements in a deque after deletion: " ) ;
display ( arr ) ;

n = count ( arr ) ;
printf ( "\nTotal number of elements in deque: %d", n ) ;

getch( ) ;
}

/* adds an element at the beginning of a deque */
void addqatbeg ( int *arr, int item, int *pfront, int *prear )
{
int i, k, c ;

if ( *pfront == 0 && *prear == MAX - 1 )
{
printf ( "\nDeque is full.\n" ) ;
return ;
}

if ( *pfront == -1 )
{
*pfront = *prear = 0 ;
arr[*pfront] = item ;
return ;
}

if ( *prear != MAX - 1 )
{
c = count ( arr ) ;
k = *prear + 1 ;
for ( i = 1 ; i <= c ; i++ )
{
arr[k] = arr[k - 1] ;
k-- ;
}
arr[k] = item ;
*pfront = k ;
( *prear )++ ;
}
else
{
( *pfront )-- ;
arr[*pfront] = item ;
}
}

/* adds an element at the end of a deque */
void addqatend ( int *arr, int item, int *pfront, int *prear )
{
int i, k ;

if ( *pfront == 0 && *prear == MAX - 1 )
{
printf ( "\nDeque is full.\n" ) ;
return ;
}

if ( *pfront == -1 )
{
*prear = *pfront = 0 ;
arr[*prear] = item ;
return ;
}

if ( *prear == MAX - 1 )
{
k = *pfront - 1 ;
for ( i = *pfront - 1 ; i < *prear ; i++ )
{
k = i ;
if ( k == MAX - 1 )
arr[k] = 0 ;
else
arr[k] = arr[i + 1] ;
}
( *prear )-- ;
( *pfront )-- ;
}
( *prear )++ ;
arr[*prear] = item ;
}

/* removes an element from the *pfront end of deque */
int delqatbeg ( int *arr, int *pfront, int *prear )
{
int item ;

if ( *pfront == -1 )
{
printf ( "\nDeque is empty.\n" ) ;
return 0 ;
}

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

if ( *pfront == *prear )
*pfront = *prear = -1 ;
else
( *pfront )++ ;

return item ;
}

/* removes an element from the *prear end of the deque */
int delqatend ( int *arr, int *pfront, int *prear )
{
int item ;

if ( *pfront == -1 )
{
printf ( "\nDeque is empty.\n" ) ;
return 0 ;
}

item = arr[*prear] ;
arr[*prear] = 0 ;
( *prear )-- ;
if ( *prear == -1 )
*pfront = -1 ;
return item ;
}

/* displays elements of a deque */
void display ( int *arr )
{
int i ;

printf ( "\n front->" ) ;
for ( i = 0 ; i < MAX ; i++ )
printf ( "\t%d", arr[i] ) ;
printf ( " <-rear" ) ;
}

/* counts the total number of elements in deque */
int count ( int *arr )
{
int c = 0, i ;

for ( i = 0 ; i < MAX ; i++ )
{
if ( arr[i] != 0 )
c++ ;
}
return c ;
}