二进制和十进制如何相互转换？？

Function Bin2Dec(num) '二进制转十进制
dim a, i, b
a = len(num)
for i = 0 to a - 1
b = b + 2 ^ i * mid(num, a - i, 1)
next
Bin2Dec = b
End Function

Function Dec2Bin(num) '十进制转二进制
dim a, b
a = num
do
if a mod 2 = 0 then
b = "0" & b
else
b = "1" & b
end if
a = int(a / 2)
loop until a = 0
Dec2Bin = b
End Function