Editing C (programming language) (section)

=== Array–pointer interchangeability ===
The subscript notation <code>x[i]</code> (where <code>x</code> designates a pointer) is [[syntactic sugar]] for <code>*(x+i)</code>.<ref name="Raymond1996">{{cite book |last1=Raymond |first1=Eric S. |author-link=Eric S. Raymond |title=The New Hacker's Dictionary |edition=3rd |url={{GBurl|id=g80P_4v4QbIC|p=432}} |access-date=August 5, 2012 |date=October 11, 1996 |publisher=MIT Press |isbn=978-0-262-68092-9 |page=432 }}</ref> Taking advantage of the compiler's knowledge of the pointer type, the address that <code>x + i</code> points to is not the base address (pointed to by <code>x</code>) incremented by <code>i</code> bytes, but rather is defined to be the base address incremented by <code>i</code> multiplied by the size of an element that <code>x</code> points to.  Thus, <code>x[i]</code> designates the <code>i+1</code>th element of the array.

Furthermore, in most expression contexts (a notable exception is as operand of <code>[[sizeof]]</code>), an expression of array type is automatically converted to a pointer to the array's first element. This implies that an array is never copied as a whole when named as an argument to a function, but rather only the address of its first element is passed. Therefore, although function calls in C use [[pass-by-value]] semantics, arrays are in effect passed by [[reference (computer science)|reference]].

The total size of an array <code>x</code> can be determined by applying <code>sizeof</code> to an expression of array type. The size of an element can be determined by applying the operator <code>sizeof</code> to any dereferenced element of an array <code>A</code>, as in <code>n = sizeof A[0]</code>. Thus, the number of elements in a declared array <code>A</code> can be determined as <code>sizeof A / sizeof A[0]</code>. Note, that if only a pointer to the first element is available as it is often the case in C code because of the automatic conversion described above, the information about the full type of the array and its length are lost.