Objective-C Fundamentals

300 APPENDIX B The basics of C
x but each clearly had a different impact on the larger expression they’re contained in
because both y and z evaluate to the value 16 even though the value of x changes
value after each statement is executed.
The expression y = ++x + 10 can be rewritten as y = (x = x + 1) + 10, which is similar
in nature to the expressions discussed in the previous section. Variable x (which starts
off as the value 5) is assigned a new value of x + 1, resulting in x equaling 6. This
updated value is then added to 10 to produce the result of 16, which is then stored in
variable y.
The next expression, y = x++ + 10, performs the same set of operations but in a different
order. In this case, the current value of x (which at the start of executing this
line is 6) has 10 added to it. This results in variable z being assigned the value 16, and
it’s only after this assignment that variable x is increased by 1.
The pre-increment operator (++x) increases the value of the variable and then
uses the result in the larger expression, while the post-increment operator (x++)
uses the current value of the variable in the larger expression and then increments
the variable after the fact. Similar --x and x-- operators perform pre- and postdecrement
operations.
B.2.5
Operator precedence
Some expressions are ambiguous and can be interpreted in multiple ways. For example,
should the following statement result in variable x having the value 20 or 14?
int x = 2 + 3 * 4;
int y = (2 + 3) * 4;
int z = 2 + (3 * 4);
C implements a set of precedence rules that specify the order in which expressions
should be calculated (multiplication and division before addition and subtraction, for
example). These rules mean that variable x will have the value 14.
If you need to override the precedence rules, you can use parentheses to explicitly
control the order in which operations are calculated, as demonstrated by variables
y and z.
This concludes our look at expressions and how to specify them in a C-based
application. One type of expression that deserves greater attention is the conditional
expression. Expressions of this form enable you to check the state of the data
stored in an application and come up with a single Boolean (true or false) value
that represents the truth of a potentially complex situation. What we haven’t covered
is how to use such a value to change the behavior and flow of execution in an
application. C provides the answer in a set of statements collectively called the conditional
statements.
B.3 Conditional statements
Applications that execute a fixed sequence of commands are not the most exciting or
practical. Invariably, an application of any complexity must make conditional decisions