8.1.5 Manipulating 2d Arrays -

: Remember that matrix.length gives the number of rows , while matrix[0].length gives the number of columns .

This requires a mental shift. The elements in a column are spread across different arrays. To access column 2, you must iterate through the rows while keeping the column index constant. 8.1.5 manipulating 2d arrays

for (int r = 0; r < grid.length; r++) for (int c = 0; c < grid[r].length; c++) sum += grid[r][c]; : Remember that matrix