Was ist schneller? function oder 3x stringreplace?

[Helmi]

Wieso funktioniert denn das?

Delphi-Quellcode:

   CurrentChar := PChar(aSearchString); 

   for i := 1 to Length(aSearchString) do 
   begin 
      if CurrentChar^ in ['0'..'9'] then 
      begin 
         inc(NumberLength); 

         if not NumberFound then 
         begin 
            NumberStart := i; 
            NumberFound := True; 
         end; 
      end 
      else if NumberFound then 
         break; 

      inc(CurrentChar); 
   end;

Woher weiss er welcher char in der schleife bearbeitet werden soll?