Last lesson we made a promise: we stop repeating the printing. The tool is a function: a named piece of code you write once and call as many times as you like.

func formatItem(title string, pages int, read bool) string {
	return fmt.Sprintf("Book: %s | pages: %d | read: %v", title, pages, read)
}

Anatomy:

• func + a name — like a variable, but it stores an action instead of a value.
• Parameters in the parentheses — the inputs, with types: title string, pages int, read bool.
• Return type after the parentheses — what comes out: here a string.
• return — hands the result back to the caller.

You call it like this: line := formatItem("Dune", 412, true) — the parameters fill from the arguments in the same order.

Scope: parameters and variables created inside live only between the function's { }. Once the function ends they are gone — which is why two functions can happily use the same variable name.

The course rule from today on: main does almost nothing itself — it only calls functions. The logic lives in functions with clear names.