How to read from registry key in a cycle

I'm making an installer that adds features to a previously installed program, kind of add-on.

The must-present program adds registry keys according to the release.

I want to read this key and check if the to-be installed add-on is compatible with the present version of the program to allow it to be installed, otherwise I want to display a notification message informing that no compatible version is present.

My code until now is:

Result: = RegKeyExists (HKEY_LOCAL_MACHINE, 'Software\Wow6432Node\Program\5.0.0');  
     if Result = False Then  
        MsgBox ('Error: NOT program is installed', mbInformation, MB_OK);  
     if Result = True Then      
        .....`

Version numbering goes like 5.0.0, 5.0.1, 5.0.2, 5.0.3 ....

I want to check for a bunch of compatible versions on a cycle, how can I achieve this?

If I understand correctly, you want to check for a number of compatible installed versions and proceed only if a compatible version is installed?

You have different choices, if the number of target versions is not to high, the fastest is to check for a series of pre-defined versions, like this:

Warning This is not an elegant solution, just working and simple to code, being warned, look:

const
  MaxCompatibleVersions = 4;

function CompatibleVersionPresent: Boolean;
var
  I: Integer;
  CompatibleVersions: array[1..4] of string;
begin
  CompatibleVersions[1] := '5.0.0';
  CompatibleVersions[2] := '5.0.1';
  CompatibleVersions[3] := '5.0.2';
  CompatibleVersions[4] := '5.1.0';
  Result := False;
  for I := 1 to MaxCompatibleVersions do
  begin
    Result := Result or RegKeyExists(HKEY_LOCAL_MACHINE, 'Software\Wow6432Node\Program\' + CompatibleVersions[I]);  
    if Result then 
      Break;
  end;
  if not Result then
    MsgBox('Error, a compatible version of the program is not present, the plugin cannot be installed', mbError, MB_OK);
end;

procedure InitializeWizard();
begin
  if not CompatibleVersionPresent then
    Abort;
end;

Improving this is is an exercise up to the reader, some hints:

• Do not store the compatibility list as a part of the installer script, include a text file with the compatible versions list. You can extract the file to a temporary place at runtime and perform the check against that file
• Read the installed version only once and compare with the pre-defined array of strings or StringList loaded from the file.
• A better solution, IMHO, would be to read the installed version, parse it (or store it in different fields for major, minor, release) and then perform a kind of range check. What is a valid check is up to you and the constraints imposed by your compatibility schema.