Queue Using Arrays in C

# include <stdio.h>
# define SIZE 10

int arr[ SIZE ], front = -1, rear = -1, i;

void enqueue() ;
void dequeue() ;
void display() ;
 


int main()
{
    int ch ;

    do
        {
            printf( "\n[1].ENQUEUE [2].DEQUEUE [3].Display [4].Exit\n" ) ;
            printf( "Enter your choice [1-4] : " ) ;
            scanf( "%d", &ch ) ;

            switch ( ch )
                {

                case 1 :
                    enqueue() ;
                    break ;

                case 2 :
                    dequeue() ;
                    break ;

                case 3 :
                    display() ;
                    break ;

                case 4 :
                    break ;

                default :
                    printf( "Invalid option\n" ) ;
                }
        }
    while ( ch != 4 ) ;
}




void enqueue()
{
    if ( rear == SIZE - 1 )
        {
            printf( "Queue is full (overflow)\n" ) ;
            return ;
        }

    rear++ ;
    printf( "Enter the element to ENQUEUE : " ) ;
    scanf( "%d", &arr[ rear ] ) ;

    if ( front == -1 )
        front++ ;
}





void dequeue()
{
    if ( front == -1 )
        {
            printf( "Queue is empty (underflow)\n" );
            return ;
        }

    printf( "The DEQUEUE element is : %d\n", arr[ front ] ) ;

    if ( front == rear )
        front = rear = -1 ;
    else
        front++ ;
}





void display()
{
    if ( front == -1 )
        {
            printf( "Queue is empty (underflow)\n" ) ;
            return ;
        }

    printf( "The elements in queue are : FRONT -> " ) ;

    for ( i = front ; i <= rear ; i++ )
        printf( " … %d", arr[ i ] ) ;

    printf( " … <- REAR\n" ) ;
}