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This section describes the rules that the text interpreter uses when it tries to convert a string into a number.
Let <digit> represent any character that is a legal digit in the current number base(28).
Let <decimal digit> represent any character in the range 0-9.
Let {a b} represent the optional presence of any of the characters in the braces (a or b or neither).
Let * represent any number of instances of the previous character (including none).
Let any other character represent itself.
Now, the conversion rules are:
By default, the number base used for integer number conversion is given
by the contents of the variable base
. Note that a lot of
confusion can result from unexpected values of base
. If you
change base
anywhere, make sure to save the old value and restore
it afterwards. In general I recommend keeping base
decimal, and
using the prefixes described below for the popular non-decimal bases.
doc-dpl doc-base doc-hex doc-decimal
Gforth allows you to override the value of base
by using a
prefix(29) before the first digit
of an (integer) number. Four prefixes are supported:
&
-- decimal
%
-- binary
$
-- hexadecimal
'
-- base max-char+1
Here are some examples, with the equivalent decimal number shown after in braces:
-$41 (-65), %1001101 (205), %1001.0001 (145 - a double-precision number), 'AB (16706; ascii A is 65, ascii B is 66, number is 65*256 + 66), 'ab (24930; ascii a is 97, ascii B is 98, number is 97*256 + 98), &905 (905), $abc (2478), $ABC (2478).
Number conversion has a number of traps for the unwary:
base @ .
-- the number base is always 10 in the current number
base. Instead, use something like base @ dec.
bin
but it does not set the number base!
It is used to specify file types.
.
of a double-precision number to be the
final character in the string. Gforth allows the .
to be
anywhere after the first digit.
base
is required to be decimal when
converting floating-point numbers. In Gforth, number conversion to
floating-point numbers always uses base &10, irrespective of the value
of base
.
You can read numbers into your programs with the words described in 5.18.5 Input.
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