c语言 十六进制转换为二进制 用函数做

我不会C语言，只会delphi
我给你一段delphi语言的代码吧，我刚写的
procedure TForm1.Button1Click(Sender: TObject);
var s,s1:string;
m,i:integer;
begin
s:=edit1.text;
m:=length(s);//16进制字符串的长度
S1:='';
for i:=1 to m do
begin
case s[i] of //对于16进制的每一位，进行下面的操作
'0': S1:='0000'+S1;
'1': S1:='0001'+S1;
'2': S1:='0010'+S1;
'3': S1:='0011'+S1;
'4': S1:='0100'+S1;
'5': S1:='0101'+S1;
'6': S1:='0110'+S1;
'7': S1:='0111'+S1;
'8': S1:='1000'+S1;
'9': S1:='1001'+S1;
'A': S1:='1010'+S1;
'B': S1:='1011'+S1;
'C': S1:='1100'+S1;
'D