I am am writing a program that validates certain user inputs in a wages program. One of the inputs is a taxcode - this comprises of 3 digits and 1 letter ('L' or 'H').

How can I validate the user input taxcodes so that only taxcodes that consist of 3 digits and 1 letter (l or H) are accepted?

: I am am writing a program that validates certain user inputs in a wages program. One of the inputs is a taxcode - this comprises of 3 digits and 1 letter ('L' or 'H').
:
: How can I validate the user input taxcodes so that only taxcodes that consist of 3 digits and 1 letter (l or H) are accepted?
:
:
:

You might want to modify this to fit your needs:

function inputTaxCode : String;
var s   : String;
      ch : Char;
begin
  s := '';
  while (true) do begin

    {wait until keypressed}
    repeat until (keypressed);
    {get the key}
    ch := readKey;

    {only process ASCII keys}
    if NOT(ch = 0) then begin
      ch := UPCASE(ch);

     {return}
      if (ch = #13) AND (length(s) = 4) then begin
        inputTaxCode := s;
        exit;

     {backspace}
      end else if (ch = #8) AND NOT(length(s) = 0) then begin
        s := copy(s, 1,length(s)-1);
        write(#8);

      {digits and L and H}
      end else  if ((ch >= '0') AND (ch <= '9') AND (length(s) < 3)) OR
          (((ch = 'L') OR (ch = 'H')) AND  (length(s) = 3)) then begin
         s := s + ch;
         write(ch);
       end;

    end else ch := readKey; {ignore the extended keycodes}
  end;
end;

There are sure some syntax errors in the code above - I didn't check it with pascal.

tron.

: I am am writing a program that validates certain user inputs in a wages program. One of the inputs is a taxcode - this comprises of 3 digits and 1 letter ('L' or 'H').
:
: How can I validate the user input taxcodes so that only taxcodes that consist of 3 digits and 1 letter (l or H) are accepted?
:
:
:


my version:

{Returns TRUE if ch is a number}
function IsDigit(ch:char):boolean;
begin
     IsDigit := (ch in ['0'..'9']);
end;

{Returns TRUE if ch is either 'H' or 'L'}
function IsHL (ch:char):boolean;
begin
     IsHL := ((UpCase(ch) = 'H') or (UpCase(ch) = 'L'));
end;


{Returns TRUE if tax code is valid}
function TaxCodeValid(s:string):boolean;
var
   result:boolean;
   i:byte;
begin
     result:=true;

     {Remove any spaces from the beginning of the string}
     while (s[1] = #32) and (byte(s[0]) > 0) do delete(s,1,1);

     {Remove any spaces from the end of the string}
     while (s[byte(s[0])] = #32) and (byte(s[0]) > 0) do dec(byte(s[0]));

     if byte(s[0]) <> 4 then result:=false
     else
     begin
          for i:=1 to 3 do
          if (not IsDigit(s[i])) then result:=false;
          if (not IsHL (s[4])) then result:=false;
     end;
     TaxCodeValid:=result;

end;

begin
     writeln(TaxCodeValid('123H'));
     writeln(TaxCodeValid('1234'));
end.