Expressions

An expression is a combination of values, variables, and/or other expressions separated by operators, or simply a single value or variable.

Table 3-2: Expression Examples

Table 3-2: Expression Examples
'Friday'	1 + 3
$A + $B	4.0
$E = $M * $C^2	$String1 EQ $String2
$Browser.type	$Variable = 4 + 3
$Form.name	$X = $A + $B
$Variable = (34 GE 341)	$LastName = 'Smith'

Values

Variables of the form $varname

String literals of the form 'string text'

Numbers of the form x or x.x

Numbers using scientific notation of the form xEy, xey, xDy, or xdy, where x is any real number and y is a positive or negative exponent. For example, 2E6 is the same as 2 * 10⁶. Note that in ION Script there is no difference between the characters e, E, d, and D.

Booleans of the form TRUE, FALSE, true, or false. For example, $A EQ TRUE

Expression Types

Numeric expressions

Boolean expressions

String expressions

Numeric Expressions

Numeric expressions are expressions that evaluate to a number. The following are examples of numeric expressions:

1 + 3

4.0

$a + $b (assuming a and b are both numbers)

$Mouse.x

Numbers can be one of two types: DOUBLE (double precision, such as 1.2345) or INT (integer, such as 1).

All numeric expressions are evaluated as double-precision values, regardless of whether the variables or values in the expression are integers or double-precision values. For example, if you declare variables A and B as integers, the result of $A+$B will be a double. If, however, you assign the result of $A+$B to a variable that was declared as an integer, then the result will be an integer.

Boolean Expressions

Boolean expressions are expressions that return a boolean value, that is, true or false. The values used in the expression are numbers or strings. The operators that return boolean values are:

$Temp GE 212

$X EQ $Y

$Mouse.x GT 128

$Form.UserEntry EQ 'Form1'

$Name ISTYPE 'STR'

$BOOL1 AND $BOOL2

If you declare a variable as a BOOL, and then later reassign it a numeric value, the variable is assigned a value of FALSE if the expression evaluates to zero, and TRUE otherwise. For example, if $C was declared as type BOOL, and later reassigned the value $C = $A + $B, then $C would be assigned the value FALSE if $A + $B evaluates to 0, and TRUE if $A + $B evaluates to anything other than 0.

String Expressions

String expressions are expressions that return strings. Strings can be used with five operators: EQ, NE, +, CONTAINS, and ISTYPE. The + operator is used to concatenate, or combine, two strings. For example, the expression 'Hello' + ' World!' yields 'Hello World!'.

'Your name is ' + $Name

'ITT'

$Form.variable (All $Form variables are treated as strings. See INPUT for information on when you should declare variables corresponding to $Form variables.)

5 + 'gallons'. When adding a numeric value to a string value, the result of the numeric value is concatenated as a string to the string value.

$Name CONTAINS 'Smith'

If you declare a variable as type string and assign it a numeric value, the number will be converted to double-precision and then to a string. For example, the following code creates a string variable and assigns the value 35.4:

<VARIABLE_DECL NAME="A" VALUE="35.4" TYPE="STR"/>

If you write the value of this variable to the page, it will read as 35.40 instead of 35.4. To prevent the number from being converted to a double-precision value, enclose it in single quotation marks as follows:

<VARIABLE_DECL NAME="A" VALUE=" '35.4' " TYPE="STR"/>

IDL Online Help (March 06, 2007)