problem 6 next()

    public CrossIterator(SQLStatement stmt) throws DatabaseException {
        /* not yet implemented */
        int numTables = stmt.numTables();
        int colCTR = 0;
        int refMark = 0;                // refMark is used to set the for loop iterator at the
                                        // correct index to store the next column object
        int ctr = 0;
        int sizeOfcolArry = 0;
        int colAdvance = 0;
        /**
         * loop to get sum of columns from each table
         * in order to dynamically size columns array
         */
        for (int i = 0; i < numTables; i++) {
            sizeOfcolArry += stmt.getTable(i).numColumns(); // count number of columns in each table
        }
        this.columns = new Column[sizeOfcolArry];
        this.tableIter = new TableIterator[stmt.numTables()];
        /* *
         *   loop over num tables in the stmt
         */
        for (int i = 0; i < numTables; i++) {
            Table table = new Table(stmt.getTable(i).getName()); // create table object to store table info
            table.open();
            TableIterator iter = new TableIterator(stmt,table,false);
            colCTR = ctr + table.numColumns();                         // count number of columns in each table
            tableIter[i] = iter;                                 // assign iter to tableIter array
            /**
             * loop to store column objects into column array
             */
            ctr = 0;
            for (int j = refMark; j < colCTR; j++) {
                    this.columns[j] = table.getColumn(colAdvance);
                    colAdvance++;
                    ctr++;
            }
            colAdvance = 0;
            refMark = ctr ;           // update refMark

        }
        this.where = stmt.getWhere();
        if (this.where == null)
            this.where = new TrueExpression();   // set were clause

        this.numTuples = 0;
    }

    public boolean next() throws DeadlockException, DatabaseException {
        /* not yet implemented */
//      for (int i = 0; i < tableIter.length-1; i++) {
//            tableIter[i].first();                      // set all iterators to first row
//        }

        if (tableIter.length > 1){
            for (int i = tableIter.length; i > 0 ; i--) { // start at the right most cell
                // If this is the first time the method has been called,
                // preload the first row of R.
                if (numTuples == 0) {
                   if (!tableIter[0].first())
                       return false;   // R is empty
                }

                // Advance the table iterators as much as needed to get
                // to a combination of rows from R and S that satisfies the
                // WHERE clause.
                do {
                    if (!tableIter[i].next()) {
                        // We've paired all rows of S with the current row of R,
                        // so reset S to its first row...
                        if (!tableIter[i].first())
                            return false;   // S is empty

                        // ...and advance to R's next row (if any).
                        if (!tableIter[i-1].next())
                            return false;   // no more rows in R, so we're done
                    }

                } while(!this.where.isTrue());

            }

        }


        this.numTuples++;
        return true;
    }