Variables & Expressions

Variables store data that flows between activities. Expressions let you compute values, build strings, and make comparisons. Getting the format right is the most common source of beginner errors — this page covers all rules precisely.

Variable Types

Type	Description	Example default value
`String`	Text	`"Hello"`
`Int32`	32-bit integer	`0`
`Int64`	64-bit integer (large numbers)	`0`
`Double`	Floating-point decimal	`0.0`
`Boolean`	True or false	`false`
`DateTime`	Date and time value	`DateTime.Now`
`DataTable`	Tabular data (rows + columns)	empty table
`DataRow`	A single row from a DataTable	—
`StringArray`	Array of strings	empty
`Int32Array`	Array of integers	empty
`List`	Generic list of objects	empty
`Object`	Any value (avoid when possible)	—

Declaring Variables

Open the Variables Panel at the bottom of the designer
Click + Add Variable (or press Alt+N)
Set Name (camelCase recommended — e.g., invoiceTotal), Type, and optional Default Value
Scope is Workflow by default (available everywhere); set to Local for loop-scoped variables

Arguments (for Invoke Workflow)

Use the Arguments tab in the Variables Panel to define parameters that callers pass in. Arguments have a direction:

Direction	Meaning
In	Caller supplies a value; sub-workflow reads it
Out	Sub-workflow writes a value; caller captures it
In/Out	Both — caller provides an initial value and gets the modified value back

Value Format Rules

String literals must be quotedIn the Value field of Assign, always wrap text in double quotes: "Hello World". Bare text like Hello World (without quotes) is treated as a variable name and will cause an "Unknown variable" error at runtime.

Type	Correct format	Example
String literal	`"double quoted"`	`"Processing complete"`
Empty string	`""`	`""`
Integer	bare number	`42`
Decimal	bare number	`3.14`
Boolean	`true` or `false`	`true`
Variable reference	`${name}`	`${invoiceTotal}`
Template string	`"text ${var}"`	`"Hi ${customerName}"`
Arithmetic	`${a} + ${b}`	`${subtotal} * 1.18`

Expressions in Conditions (If / While)

workflow

1	${score} >= 90
2	${count} == 0
3	${status} == "Active"
4	${age} >= 18 && ${age} <= 65
5	${a} == "X" \|\| ${a} == "Y"
6	!${isLoggedIn}

Variable Picker

Press Ctrl+Space in any property field to open the variable picker. It lists all in-scope variables with their types, letting you insert references without typing.

Type ConversionWhen you call Assign with a value that doesn't match the declared type, Studio automatically converts it (e.g., assigning 42 to a String variable produces "42"). The Variables Panel shows a yellow warning when a type conversion is lossy (e.g., Double → Int32).