If P is a two-dimensional array having 10 rows and 20 columns, then which of…

Concept

For a declaration T P[R][C], the expression P converts to a pointer to a row of C elements of type T.

Array subscripting follows a[b] == *(a + b). Arithmetic on P moves by whole rows; after a row is dereferenced and decays to T*, arithmetic moves by individual elements.

Application

1. With P[2][5], P[2] selects row 2 and the second subscript selects its element at offset 5.

2. With * (* (P + 2) + 5), P + 2 reaches row 2, the inner dereference exposes that row, + 5 reaches offset 5 after decay, and the outer dereference yields the element.

3. With *(P[2] + 5), P[2] is the row-2 array; after decay, adding 5 and dereferencing yields its element at offset 5.

4. With *(P + 2 + 5), addition is left-associative, so it is *(P + 7). Because P still points to rows during both additions, this denotes row 7 rather than an individual element in row 2.

Cross-check

The expressions P[2][5], * (* (P + 2) + 5), and *(P[2] + 5) each yield a T lvalue. In contrast, *(P + 2 + 5) yields a T[20] row lvalue that decays to T* in most expressions.

Result

Therefore, *(P + 2 + 5) cannot be used to access the element at row 2, column 5.