8.5

Working with expressions
Expressions, variables, operators, and functions combine to form a programming language
that you can use to create interactive presentations with built-in logic. For most projects,
you will not need expressions; the controls in the Interactive palette are sufficient to build
most types of multimedia presentations. However, for advanced users who want more
control, expressions provide extra power.
Understanding expressions
An expression is a short set of instructions that tells an interactive presentation to do
something. For example:
Box1.SetOpacity(50)
This expression tells an interactive presentation to set the opacity of the picture box named
"Box1" to 50% opaque.
Each expression is made up of several parts. The following five components can go into
an expression:
• Parameters
• Variables
• Operators
• Functions
• Objects
In this example, "Box1" is an object, "SetOpacity" is a function, and "50" is a parameter.
By combining these parts in a specific order, we create an expression that tells an interactive
presentation to place the text into the box.
Parameters
A parameter is a piece of information. A parameter can be anything from an integer to an
interactive object. A variable type is available for each type of parameter.
Variables
A variable is a place to store a piece of information. You can think of it as a "slot" into
which you can store a value. Presentation layouts support the following types of variables:
• Integer: A whole number from –2,147,483,648 to 2,147,483,647 (inclusive).
• Decimal: A fractional number from –9x10306 to 9x10306 with a precision of 15 decimal
places.
• String: A series of up to 255 letters, numbers, and punctuation characters.
• Boolean: True or false.
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INTERACTIVE LAYOUTS