Variables and Compose

Introduction to Power Automate

Anushika Agarwal

Cloud Data Engineer

Why store values?

Real Power Automate Manually trigger a flow card open on its Parameters tab with a red highlight box around the Parameters tab label, the Settings, Code view, and About tabs visible to its right, and a plus Add an input affordance below

Reuse a value across multiple actions (e.g. a trigger input)
Update a counter or build a string as the flow runs
Compare values later in Conditions or Switch

Initialize variable

Always the first variable action in a flow
Declares the name, type, and starting value
Six types: String, Integer, Float, Boolean, Array, Object
One Initialize action per variable: each variable gets its own

Golden rule: Initialize before you use.

Real Power Automate Initialize variable action card cropped to its parameters panel, with the Name field, Type dropdown, and Value field each annotated with a red box to highlight the three slots called out in the bullets

Updating variables

Power Automate Variable actions panel showing all six actions: Initialize variable, Set variable, Append to string variable, Append to array variable, Increment variable, Decrement variable

Set → replace the value
Append to string or array → add to the end
Increment or Decrement → add or subtract from a number

Heads up: Set inside a loop means only the last item survives. Use Append.

Compose

Conceptual illustration contrasting a sealed labeled jar with a fixed value (Compose) and an open box with arrows showing values flowing in and out (Variable)

Write-once value store: you set it once, it never changes
No type declaration: Compose infers the type automatically
Goes anywhere: inside loops, inside branches (unlike Initialize Variable)
Best used as an expression debugger: drop one in, run the flow, read the output in run history, remove it

Variables vs Compose: when to use each

Aspect	Compose	Variable
Value	Write-once, fixed for the run	Updatable across the flow
Type declaration	Not required, inferred	Required at initialization
Placement	Anywhere in the flow	Top level only
Performance in loops	Lightweight, safe in parallel	Can cause locking in parallel
Best for	Snapshots and expression debugging	Counters, builders, accumulators

Value needs to change across steps or iterations → Variable
Value is computed once and reused unchanged → Compose

Let's practice!

Introduction to Power Automate