// IBAN = International Bank Account Number

// Example : CH10002300A1023502601

function ChangeAlpha(input: string): string;

 // A -> 10, B -> 11, C -> 12 ...

var  

 a: Char;

begin

 Result := input;

 for a := 'A' to 'Z' do

 begin

   Result := StringReplace(Result, a, IntToStr(Ord(a) - 55), [rfReplaceAll]);

 end;

end;

function CalculateDigits(iban: string): Integer;

var  

 v, l: Integer;

 alpha: string;

 number: Longint;

 rest: Integer;

begin

 iban := UpperCase(iban);

 if Pos('IBAN', iban) > 0 then

   Delete(iban, Pos('IBAN', iban), 4);

 iban := iban + Copy(iban, 1, 4);

 Delete(iban, 1, 4);

 iban := ChangeAlpha(iban);

 v := 1;

 l := 9;

 rest := 0;

 alpha := '';

 try

   while v <= Length(iban) do

   begin

     if l > Length(iban) then

       l := Length(iban);

     alpha := alpha + Copy(iban, v, l);

     number := StrToInt(alpha);

     rest := number mod 97;

     v := v + l;

     alpha := IntToStr(rest);

     l := 9 - Length(alpha);

   end;

 except

   rest := 0;

 end;

 Result := rest;

end;

function CheckIBAN(iban: string): Boolean;

begin

 iban := StringReplace(iban, ' ', '', [rfReplaceAll]);

 if CalculateDigits(iban) = 1 then

   Result := True

 else

   Result := False;

end;