Decimal to Hex and back again

const
  searchstring = '0123456789ABCDEF';

procedure decimaltohex;
var
  decimal : integer;
  remainder : integer;
  value : string;
begin
 value := '';
 write('Enter a decimal number:');
 readln(decimal);
 while decimal <> 0 do
   begin
   remainder := decimal and $F;
   decimal := decimal shr 4;
   // remainder := decimal mod 16;
   // decimal := decimal div 16;
   value := searchstring[remainder+1]+value;
 end;
 writeln('Hex value is:',value);
 readln;
end;


procedure hextodecimal;
var
  hex : string;
  value : integer;
  i,position:integer;
begin
 value := 0;
 write('Enter a Hex number:');
 readln(hex);
 for i  := 1 to length(hex) do
   begin
       position := pos(hex[i],searchstring)-1;
       value := (value * 16) + position;
   end;
   writeln('Decimal value is:',value);
   readln;
end;


//-----------------------------------------------------------------------------------------

function dectobinary(decimalno:integer) : string;
var
   binarystring : string;
begin
   binarystring := '';
   while decimalno > 0 do
   begin
     if decimalno and $1 = 0 then
         binarystring := '0' + binarystring
     else
         binarystring := '1' +binarystring;

     decimalno := decimalno shr 1;
   end;
   dectobinary := binarystring;
end;

function binarytodec(binarystring:string) : integer;
var
  decimalno : integer;
  i : integer;
  m : integer;
begin
  decimalno := 0;
  m:= 1;
  for i := length(binarystring) downto 1 do
  begin
      if binarystring[i] = '1' then
          decimalno := decimalno + m;
      m := m shl 1;
  end;
  binarytodec := decimalno;

end;
begin
   writeln(binarytodec(dectobinary(49))) ;
   readln;
end.