Objective-C Fundamentals

The basic data types
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Because variables of type int are signed by default, it’s uncommon to see the signed
qualifier used in most applications—its use is somewhat redundant.
Once you declare a variable, you can assign it a value with the assignment operator,
which is represented by an equals sign. For example, the following statements declare
a new variable called a and then assign it the value 15.
int a;
a = 15;
Because it’s common to declare a variable and then assign it an initial value, both
statements can be combined:
int a = 15;
The value 15 used in this assignment statement is called a constant. A constant is any
value that can never change its value while the application is running. A constant
doesn’t have to be a single number; for example, the following variable declaration
also makes use of a constant value.
int a = 5 + 3;
The value calculated by the expression 5 + 3 can never result in a number other than 8.
The Objective-C compiler calculates the value of this expression during compilation
and replaces it with a single constant value.
By default, integer constants are specified in decimal, or base 10, which is the most
familiar notation for most people. It’s also possible to specify integer constants in a
number of other bases by using a special prefix in front of the number, as detailed in
table 2.1.
Table 2.1 Different ways to express the value 15 as an integer constant. Each format is identified by a
special prefix that precedes the number.
Name Base Prefix Example constant
Octal 8 0 017
Decimal 10 — 15
Hexadecimal 16 0x 0x0F
One trap new developers occasionally make is to include a leading zero at the start of
a decimal number. As far as Objective-C is concerned, 017 isn’t the same value as 17.
The leading zero in front of the first constant means the number is interpreted as an
octal (base 8) number and hence equals the decimal value 15.
FACING THE LESS-THAN-IDEAL REAL WORLD
The iPhone is a vast improvement over the hardware and memory constraints of a traditional
cell phone, but it’s still constrained by real-world realities such as a fixed
amount of memory being available to applications. In an ideal world, developers