points at an array or a single instance, and the second problem is whether the pointer references a valid item upon entry.&nbsp; The historical third problem, whether it is legal to alter the contents of a dereferenced pointer, is addressed by the ANSI</font> <font face="Ohlfs,Courier" size="-1">const</font> <font face="Times">declarator.</font>

<p><font face="Times">Objective-C offers three new keywords to address the first and second problems:</font> <font face="Ohlfs,Courier" size="-1">in</font><font fa