HP C/iX Reference Manual (31506-90011)

Chapter 5 61
Expressions
Array Subscripting
Array Subscripting
A postfix expression followed by the [ ] operator is a subscripted reference to a single
element in an array.
Syntax
postfix-expression [ expression ]
Description
One of the operands of the subscript operator must be of type pointer to T (T is an object
type), the other of integral type. The resulting type is T.
The [ ] operator is defined so that E1[E2] is identical to (*((E1)+(E2))) in every
respect. This leads to the (counterintuitive) conclusion that the [ ] operator is
commutative. The expression E1[E2] is identical to E2[E1].
C's subscripts run from 0 to n-1 where n is the array size.
Multidimensional arrays are represented as arrays of arrays. For this reason, the notation
is to add subscript operators, not to put multiple expressions within a single set of
brackets. For example, int x[3][5] is actually a declaration for an array of three objects.
Each object is, in turn, an array of five int. Because of this, all of the following expressions
are correct:
x
x[i]
x[i][j]
The first expression refers to the 3 by 5 array of int. The second refers to an array of five
int, and the last expression refers to a single int.
The expression x[y] is an lvalue.
There is no arbitrary limit on the number of dimensions that you can declare in an array.
Because of the design of multidimensional C arrays, the individual data objects must be
stored in row-major order. As another example, the expression
a[i,j] = 0
looks as if array a were doubly subscripted, when actually the comma in the subscript
indicates that the value of i should be discarded and that j is the subscript into the a
array.