The rule of variable scope is defined simply: a variable created
inside a block (code enclosed within braces: {
and }
)
exists only inside that block. This means that a variable created inside
setup() can be used only within the
setup() block, and likewise, a variable declared
inside draw() can be used only inside the
draw() block. The exception to this rule is a
variable declared outside of setup() and
draw(). These variables can be used in both
setup() and draw() (or inside
any other function that you create). Think of the area outside of
setup() and draw() as an implied
code block. We call these variables global variables,
because they can be used anywhere within the program. We call a variable
that is used only within a single block a local
variable. Following are a couple of code examples that further
explain the concept. First:
int
i
=
12
;
// Declare global variable i and assign 12
void
setup
()
{
size
(
480
,
320
);
int
i
=
24
;
// Declare local variable i and assign 24
println
(
i
);
// Prints 24 to the console
}
void
draw
()
{
println
(
i
);
// Prints 12 to the console
}
And second:
void
setup
()
{
size
(
480
,
320
);
int
i
=
24
;
// Declare local variable i and assign 24
}
void
draw
()
{
println
(
i
);
// ERROR! The variable i is local to setup()
}