Precondition:  The function accepts an unsorted array  []  and integer size that is the size of the array.

Post condition:  Sorted array

The function performs the two direction bubble sort. It starts from the head and from the tail of the array and compares two adjusted cells. If the numbers are not in order, they are exchanged. After each pass, the array becomes shorter by one cell from the head and by one cell from the tail.  

void TwoBubbleSort ( int  size, int array [] )
{
    int current = 0;
    bool sorted = false;

           while (( current < size )&&( sorted = = false ))
            {
            int walker1 = size -1;           // walks from the tail to the head
            int walker2 = current;            // walks from the head to the tail
            sorted = true;

                    while ( walker1 > current )
                    {
                            if ( array [walker1] < array [walker1-1] )
                            {
                                sorted = false;
                                exchange ( array, walker1, walker1-1 );
                            }
                        walker1 = walker1 - 1;

                                if ( array [walker2] > array [walker2 + 1] )
                                    {
                                        sorted = false;
                                        exchange ( array, walker2, walker2 + 1 );
                                     }
                            walker2 = walker2 + 1;
                    }
                  current = current + 1 ;
                  size = size -1;
            }
}