Convert hexadecimal to binary

Hexadecimal format of a number is a reduced binary format of this number. Use HexToBin function to convert hexadecimal to binary format.

function HexToBin(HexStr: string): string;
const
  BinArray: array[0..15, 0..1] of string =
    (('0000', '0'), ('0001', '1'), ('0010', '2'), ('0011', '3'),
     ('0100', '4'), ('0101', '5'), ('0110', '6'), ('0111', '7'),
     ('1000', '8'), ('1001', '9'), ('1010', 'A'), ('1011', 'B'),
     ('1100', 'C'), ('1101', 'D'), ('1110', 'E'), ('1111', 'F'));
  HexAlpha: set of char = ['0'..'9', 'A'..'F'];
var
  i, j: Integer;
begin
  Result:='';
  HexStr:=AnsiUpperCase(HexStr);
  for i:=1 to Length(HexStr) do
    if HexStr[i] in HexAlpha then
    begin
      for j:=1 to 16 do
        if HexStr[i]=BinArray[j-1, 1] then
          Result:=Result+BinArray[j-1, 0];
    end
    else
    begin
      Result:='';
      ShowMessage('This is not hexadecimal number');
      Break;
    end;
  if Result<>'' then
   while (Result[1]='0')and(Length(Result)>1) do
     Delete(result, 1, 1);
end;