An array’s length is its number of elements. For an array object A, calculate it with `(sizeof A) / (sizeof A[0])`: divide the object’s total size by one element’s size. An omitted bound can be determined from an initializer when the initializer’s structure is known at compile time. section 6.1.3
Keep these distinctions explicit:
- If the bound is not an integer constant expression, the array is a variable-length array (VLA). VLA support has changed across C standards. section 6.1.3
- A pointer does not retain the length of the array object behind it; pointer-based functions must receive the real length separately. section 11.1.2
- Array-parameter notation such as `double const a[len]` clarifies the expected element count, even when the interface passes through a pointer. section 11.1.2
Passing a length with a pointer
For `double A[7]`, a function can sum the whole array with `sum0(7, &A[0])`, the last six elements with `sum0(6, &A[1])`, or three middle elements with `sum0(3, &A[2])`. The pointer identifies a starting element; `len` identifies how many elements to process. section 11.1.2
double E[] = { [3] = 42.0, [2] = 37.0, };
double F[] = { 22.0, 17.0, 1, 0.5, };
Compare an omitted array bound inferred from a designated initializer with an explicitly inferred four-element array. section 6.1.3
