how to read in a number in hex and convert it to binary

[Michael O'Hanrahan]

Hi, newbie question I'm afraid, but I couldn't work out how to do this from the help. I'm using Mathematica 5.2.

I've got a textfile containing about 30 thousand 256-digit numbers in hex. I need to read them in and work on them one by one. Reading them is fine using

Read["hello.txt",Expression]

Then I would like to turn each number into a fixed-length binary number, using something like

IntegerDigits[16^^p, 2, 27]

The problem is, this doesn't work. The argument of ^^ seems to need to be an actual number in hex, e.g. 16^A12B3, rather than a variable.

Given that essentially ^^ is a two-argument function, is there a way to express it as such in Mathematica?

I'm even having trouble getting the input to be accepted as a number at all . Replacing "Expression" (or "String") with "Number" or "Integer" doesn't work.

Will be grateful for any help with this.
Thanks!
Michael

[David Bailey]

You have inputted a string - say "f8" - but you really need the string
"16^^f8", which you can obtain by concatenation (the <> operator), after
which ToExpression will convert that into a number for the rest of your
calculation:

var = "f8";

int=ToExpression["16^^" <> var]

IntegerDigits[int, 2, 27]

David Bailey
http://www.dbaileyconsultancy.co.uk