9.3

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.
• Point: An x,y coordinate (for example: 10, 20). Each number must be an integer from
–2,147,483,648 to 2,147,483,647 (inclusive).
• Object: A reference to an interactive object.
Each variable has a unique name. When you use a variable's name in an expression, you're
telling an interactive presentation to go find whatever value is stored in that variable and
use that value in the expression.
For example, let's say you have an integer variable named IntVar that contains the number
6. You can then create the following expression:
Box1.Append(IntVar)
When this expression is executed (or "evaluated"), the interactive presentation will find
the value stored in the variable named "IntVar" (6) and put that value in the box named
"Box1." Afterward, the text box named "Box1" will contain the number 6.
328 | A GUIDE TO QUARKXPRESS 9.3
INTERACTIVE LAYOUTS