Many operators in C are more versatile than they appear to be at
first glance. Take, for example, the following operators:
=
++
--
+=
-=
These operators can be used in some surprising ways to make C source
code elegant and compact. (See Expressions and operators, if you
need a refresher in what they do.) All of them can form expressions
that have their own values. Such an expression can be taken as a whole
(a "black box") and treated as a single value, which can then be
assigned and compared to other expressions, in effect, "hidden" within
another expression.
The value of an expression is the result of the operation carried out in
the expression. Increment and decrement statements have a value that is
one greater than or one less than the value of the variable they act
upon, respectively.
Consider the following two statements:
c = 5;
c++;
The expression c++ in the above context has the value 6.
Now consider these statements:
c = 5;
c--;
The expression c-- in the above context has the value 4.
