Initial values for variables – PB Docs 150

Default values for variables

If you do not initialize a variable when you declare it, PowerBuilder
sets the variable to the default value for its datatype as shown
in the following table.

Specifying a literal as a initial value

To initialize a variable when you declare it, place an equal
sign (=) and a literal appropriate for that variable datatype
after the variable. For information about literals for specific
datatypes, see “Standard datatypes”.

Do not use a function’s return value

You should not initialize a variable by assigning it the return
value of a global user defined function, because it might not compile
correctly, or because it could lead to confusion about the value
assigned. For example, do not use:

PowerBuilder

integer i = f_return_one()

1	integer i = f_return_one()

Although you can use global system functions or expressions
to initialize variables with compile time values in a variable declaration
statement, for runtime value assignments, you must also declare
variables and assign their values in separate statements.

This example declares li_count as
an integer whose value is 5:

This example declares li_a and li_b as
integers and initializes li_a to 5
and li_b to 10:

This example initializes ls_method with
the string “UPS”:

This example initializes ls_headers to
three words separated by tabs:

This example initializes li_a to
1 and li_c to 100, leaving li_b set
to its default value of zero:

This example declares ld_StartDate as
a date and initializes it with the date February 1, 2004:

Specifying an expression as an initial value

You can initialize a variable with the value of an existing
variable or expression, such as:

When you do this, the second variable is initialized with
the value of the expression when the script is compiled. The initialization
is not reevaluated at runtime.

In this declaration, the value of d_date is
the date the script is compiled:

In contrast, these statements result in d_date being
set to the date the application is run:

How shared variables are initialized

When you use a shared variable in a script, the variable is
initialized when the first instance of the object is opened. When
the object is closed, the shared variable continues to exist until
you exit the application. If you open the object again without exiting
the application, the shared variable will have the value it had
when you closed the object.

For example, if you set the shared variable Count to
20 in the script for a window, then close the window, and then reopen
the window without exiting the application, Count will
be equal to 20.

When using multiple instances of windows

If you have multiple instances of the window in the example
above, Count will be equal to 20 in each instance.
Since shared variables are shared among all instances of the window,
changing Count in any instance of the window changes
it for all instances.

How instance variables are initialized

When you define an instance variable for a window, menu, or
application object, the instance variable is initialized when the
object is opened. Its initial value is the default value for its
datatype or the value specified in the variable declarations.

When to use multiple instances of windows

When you build a script for one of multiple instances of a
window, instance variables can have a different value in each instance
of the window. For example, to set a flag based on the contents
of the instance of a window, you would use an instance variable.

When to use shared variables instead

Use a shared variable instead of an instance variable if you
need a variable that:

• Keeps
  the same value over multiple instances of an object

• Continues to exist after the object is closed