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A conditional statement is used to test the
value of an expression and perform an action based
on the result. A real world example of a
conditional statement could be "If it is raining,
I should bring my umbrella". The condition is
whether or not it is raining. The action is
whether or not I bring
my umbrella. Conditional statements are invaluable when
testing for specific scenarios in Director. For
example, a conditional statement can test to see
if a QuickTime movie is playing, and if it is not
the Director movie will jump to a different frame.
'If' statements are most often used to test
one condition. 'Case' statements can test for
two
or more conditions.
For more information about if statements, see Conditional
statements: how to use "if" statements
(TechNote 16207).
Case
Statements
Case statements are like
if statements, but they are used to test against
several expressions rather than one. For example,
a case statement can be used to test which key a user has pressed. A
script is written that executes every time a user
clicks on a key, and if the key equals a key in
the case statement, an action occurs. To see an
example of a case statement that test which key is
pressed, see "case" in the Lingo dictionary, and
How
do I use KeyCode? (TechNote
15887).
Like 'if' statements, case statements have
a specific structure. First the expression being
tested is declared. Then the value or condition of
that expression is compared to several other
values or conditions.
The script below is attached to the button
in the sample movie labeled "testing the value of
x using a case statement" . A case statement is
used to trigger an alert box depending on the
value of a global variable. Once the variable is
created and a value is set, the script can be
added to a button sprite.
This script first declares the global
variable. Then on a mouseUp event, a case
statement is used to make an alert box appear on
screen. After the word "case", the expression that
is being tested (x) is entered. The word 'of'
follows.
The information on the left hand side of
the expression shows what the main expression is
being compared to. The first expression is 1, the
second expression is 2, and so on. The information
to the right of the expression is the action that
will take place if that expression is true. So,
for example, if x is equal to 3, an alert box will
appear on the screen with the text "x=3". If x
does not equal any of these expressions, nothing
will happen.
global x
on
mouseup
case (x) of
1:alert"x=1"
2:alert"x=2"
3:alert"x=3"
4:alert"x=4"
end case
end
A translation of the above code could be as
follows:
If x=1 then alert "x=1"
If x=2 then
alert "x=2"
If x=3 then alert "x=3"
If x=4
then alert "x=4"
Resources
See Global
variables (TechNote 14225) for more
information about global variables and how they
work.
Lingo
The following lingo commands were used to
create the functionality in this sample movie.
Please refer to the Lingo dictionary for more
information about these terms: case,
global, alert
Developer Notes
The sample file includes code comments and
a cast member named "Developer Notes" which
contains implementation details.
Note: This is just one of the many ways to create
this functionality in Director.
This download contains the following
file:
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case_statements.dir
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Download
the Windows zip file
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