Question

What’s the difference between declaring multidimensional arrays like this:

int a[5][5];

or this

int* a[5];

?

Which one is better to use? Thanks.

Answer 1

Both may be used to declare 2-dimensional arrays.

In the first case, 25 int elements are allocated in a contiguous region in memory.
In this case the expression a[i][j] is translated by the compiler to *(a + i*5 + j).

The second one allocates 5 pointers to int. You can make it work as a two dimensional array by allocating vectors of int and making these pointers point to these vectors.
In this case a[i][j] means get the pointer that a[i] points to, then look up the 5th element in that vector. I.e. a[i][j] is translated to *(a[i] + j).

Note that in the second case, rows need not be of the same length.