Algorithm Math Delphi

Title: Decimal to binary and vice versa
Question: How to convert binary (base2) to decimal (base10) ?
Answer:
function IntToBin(Value: LongInt;Size: Integer): String;
var
i: Integer;
begin
Result:='';
for i:=Size downto 0 do
begin
if Value and (1 shl i)0 then
Result:=Result+'1';
else
Result:=Result+'0';
end;
end;
function BinToInt(Value: String): LongInt;
var
i,Size: Integer;
begin
Result:=0;
Size:=Length(Value);
for i:=Size downto 0 do
begin
if Copy(Value,i,1)='1' then
Result:=Result+(1 shl i);
end;
end;