507
Here's what the standard says (C99 6.3.2.1/3 - Other operands - Lvalues, arrays, and function designators):
Except when it is the operand of the sizeof operator or the unary & operator, or is a string literal used to initialize an array, an expression that has type ‘‘array of type’’ is converted to an expression with type ‘‘pointer to type’’ that points to the initial element of the array object and is not an lvalue.
This means that pretty much anytime the array name is used in an expression, it is automatically converted to a pointer to the 1st item in the array.
Note that function names act in a similar way, but function pointers are used far less and in a much more specialized way that it doesn't cause nearly as much confusion as the automatic conversion of array names to pointers.
The C++ standard (4.2 Array-to-pointer conversion) loosens the conversion requirement to (emphasis mine):
An lvalue or rvalue of type “array of N T” or “array of unknown bound of T” can be converted to an rvalue of type “pointer to T.”
So the conversion doesn't have to happen like it pretty much always does in C (this lets functions overload or templates match on the array type).
This is also why in C you should avoid using array parameters in function prototypes/definitions (in my opinion - I'm not sure if there's any general agreement). They cause confusion and are a fiction anyway - use pointer parameters and the confusion might not go away entirely, but at least the parameter declaration isn't lying.