Accessing Delphi Routine Local variable

Question

How can I access the local variable of a routine from outside. Like this one eg

procedure TForm1.CalculateTax(var Amount: Double);
var 
  Tax : Double;
begin
  Tax := Amount*2.5/100;
end;

Answer 1

You can't access a local variable from outside the procedure it's declared in.

The best solution is to change your procedure to a function , and have it return the value.

Change your TForm1 declaration

type
  TForm1 = class(TForm)
  ...
  procedure CalculateTax(var Amount: Double);

to

type
  TForm1 = class(TForm)
  ...
  function CalculateTax(const Amount: Double): Double;

Change the implementation from

procedure TForm1.CalculateTax(var Amount: Double);
var 
  Tax : Double;
begin
  Tax := Amount*2.5/100;
end;

to

function TForm1.CalculateTax(const Amount: Double): Double;
begin
  Result := Amount*2.5/100;
end;

Call it like this:

Tax := CalculateTax(YourAmount);

Answer 2

My $0.02:

1) I would make this a "function" rather than a "procedure" (because it's purpose is to "return a value" - the tax amount)

2) I would not hard-code either the "amount" or "tax rate" inside the routine

3) I would not "overload" (give multiple meanings to) the variable "amount"

// Better
function TForm1.CalculateTax(purchaseAmount, taxRate: Currency) : Currency;
begin
  Result := purchaseAmount * (taxRate / 100.0);
end;