Question

I’ve bought a beginners book for visual c++ and have come the chapter which involves arrays, strings and pointers. I understand the concept, but when it comes to multidimensional arrays I got a bit lost.

Array and and pointer declaration:

double beans[3][4];
double* pbeans;

I understood this part:

*You can declare and assign a value to the pointer pbeans, as follows:

double* pbeans;
pbeans = &beans[0][0];

But when the author presents that you can assign the address for the first row/dimension by typing this statement he lost me:

pbeans = beans[0];

Why can we skip the “Address-Of” operator here?
To me the logical thing would be:

pbeans = &beans[0];

Answer 1

Because an array decays to a pointer to the first element. If we have an array called arr, then any usage of arr where an array won’t fit will generally result in arr being treated as a pointer. This is called decay.

In this case, beans[0] is an array; to be specific, an double[4]. However, as you cannot assign an array to a pointer, the array decays into a double*.

The code you provided, double* pbeans = &beans[0]; would be trying to assign a pointer to an array of doubles to a pointer to a double; that won’t work due to a type mismatch.

Also, all that aside, this doesn’t sound like a very good book; teaching arrays, strings and pointers together smells of C.