How to convert indexes of a four-dimensional array to indexes of a one-dimensional array?

Question

Programming

In two-dimensional and three-dimensional arrays a[x][y] -> a[x+y*size_x] and a[x][y][z] -> a[x+y*size_x + z*size_x*size_y] respectively . But what about the four-dimensional a[x][y][z][k]->a[????]

Answer 1

Well, just multiply all the dimensions