112. Use for EVAL
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People often get confused between VAL and EVAL on the Beeb. VAL simply tries
to treat a string as a number, so PRINT VAL("4*3+1") would give the answer 4.
The asterisk is a non-numeric character, so it and anything after it are
ignored. However, EVAL goes a step further, by attempting to evaluate the
string as a valid numeric expression, and would give the answer 13. It is
therefore possible to write a program which accepts an equation as a string,
thus opening up some interesting possibilities. Anyway, here is a more
down-to-earth use for EVAL, for which I claim no originality. If you think
about it, there isn't any obvious way to INPUT a number in Hex format; only
in Decimal. You can overcome this with the technique below.

 10 INPUT"Hex number :&" A$:A=EVAL("&"+A$)

You can also use this technique in conjunction with READ and DATA to enable
you to put Hex numbers in data statements, without bothering with the
ampersands, eg DATA 5B,3C,20,FF instead of DATA &5B,&3C,&20,&FF etc.