49.3 Gotchas in Base Conversion

Say you want to convert between octal and hex, and you type:

% 

bc ibase=8 obase=16 17

 11

It looks like something's gone haywire. 17 octal ought to be F hexadecimal, not 11. What's wrong?

In fact, since you set ibase to octal before you set obase , what you really asked for was obase equal to 16 octal (14 decimal)!

In short, always set obase before ibase , or you're in for a surprise.

Similarly, suppose you'd set ibase to 16, and want to set it back to 10. You need to type:

ibase=A

not:

ibase=10

Another thing to look out for is typing a hex digit when ibase is set to something other than 16. bc isn't smart enough to reject the input, and gives you back garbage.