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There are cases where assignments nested inside the condition can
actually make a program easier to read. Here is an example
using a hypothetical type list
which represents a list; it
tests whether the list has at least two links, using hypothetical
functions, nonempty
which is true if the argument is a nonempty
list, and list_next
which advances from one list link to the
next. We assume that a list is never a null pointer, so that the
assignment expressions are always “true.”
if (nonempty (list) && (temp1 = list_next (list)) && nonempty (temp1) && (temp2 = list_next (temp1))) … /* usetemp1
andtemp2
*/
Here we take advantage of the ‘&&’ operator to avoid executing
the rest of the code if a call to nonempty
returns “false.” The
only natural place to put the assignments is among those calls.
It would be possible to rewrite this as several statements, but that could make it much more cumbersome. On the other hand, when the test is even more complex than this one, splitting it into multiple statements might be necessary for clarity.
If an empty list is a null pointer, we can dispense with calling
nonempty
:
if ((temp1 = list_next (list))
&& (temp2 = list_next (temp1)))
…