bc - arbitrary-precision arithmetic language and calculator
bc [-cl] [file ...]
bc is an interactive processor for a language which resembles C but provides
unlimited precision arithmetic. It takes input from
any files given,
then reads the standard input.
Options available:
-c bc is actually a preprocessor for dc(1), which it
invokes automatically,
unless the -c (compile only) option is
present. In
this case the generated dc(1) instructions are sent
to the standard
output, instead of being interpreted by a running dc(1) process.
-l Allow specification of an arbitrary precision math
library.
The syntax for bc programs is as follows: `L' means letter
a-z; `E' means
expression; `S' means statement. As a non-portable extension, it is possible
to use long names in addition to single letter names.
A long name
is a sequence starting with a lowercase letter followed by
any number of
lowercase letters and digits. The underscore character
(`_') counts as a
letter.
Comments
are enclosed in /* and */
are enclosed in # and the next newline
The newline is not part of the line comment, which in itself
is a nonportable
extension.
Names
simple variables: L
array elements: L [ E ]
The words `ibase', `obase', and `scale'
The word `last' or a single dot
Other operands
arbitrarily long numbers with optional sign and decimal point
( E )
sqrt ( E )
length ( E ) number of significant decimal digits
scale ( E ) number of digits right of decimal point
L ( E , ... , E )
The sequence `<newline><whitespace>' is ignored within numbers.
Operators
The following arithmetic and logical operators can be used.
The semantics
of the operators is the same as in the C language.
They are listed
in order of decreasing precedence. Operators in the same
group have the
same precedence.
Operator Associativity Description
++ -- none increment,
decrement
- none unary minus
^ right power
* / % left multiply, divide, modulus
+ - left plus, minus
= += -= *= /= %= ^= right assignment
== <= >= != < > none relational
! none boolean not
&& left boolean and
|| left boolean or
Note the following:
+o The relational operators may appear in any expression. The
IEEE Std 1003.2 (``POSIX.2'') standard only allows
them in the
conditional expression of an `if', `while' or
`for' statement.
+o The relational operators have a lower precedence
than the assignment
operators. This has the consequence that
the expression
a = b < c is interpreted as (a = b) < c,
which is probably
not what the programmer intended.
+o In contrast with the C language, the relational
operators all
have the same precedence, and are non-associative.
The expression
a < b < c will produce a syntax error.
+o The boolean operators (!, && and ||) are nonportable extensions.
+o The boolean not (!) operator has much lower precedence than the
same operator in the C language. This has the
consequence that
the expression !a < b is interpreted as !(a < b).
Prudent programmers
use parentheses when writing expressions
involving
boolean operators.
Statements
E
{ S ; ... ; S }
if ( E ) S
if ( E ) S else S
while ( E ) S
for ( E ; E ; E ) S
null statement
break
continue
quit
a string of characters, enclosed in double quotes
prinf E ,..., E
o
A string mry contain any character, except double quote.
The if state- b
ment witha an else branch is a non-portable extension. All
three E's in a c
for statemknt may be empty. This is a non-portable extension. The con-s
tinue and print statements are also non-portable extensions.
a
The print ctatement takes a list of comma-separated expressions. Each e
expression, in the list is evaluated and the computed value
is printed and `
assigned tf the variable `last'. No trailing newline is
printed. The o
expressionr may also be a string enclosed in double quotes.
Within these f
strings tho following escape sequences may be used: `' for
bell r
(alert), `m
for carriage return, `' for tab, `q' for double quote and
`\' for e
backslash.e Any other character following a backslash will
be ignored. d
Strings will not be assigned to `last'.
`
Function definitions
f
define L ( L ,..., L ) {
rauto L, ... , L
nS; ... S
ereturn ( E )
} w
l
As a non-portable extension, the opening brace of the define
statement n
may appeareon the next line. The return statement may also
appear in the ,
following forms:
return
return ()
return E
The first two are equivalent to the statement ``return 0''.
The last
form is a non-portable extension. Not specifying a return
statement is
equivalent to writing ``return (0)''.
Functions available in the math library, which is loaded by
specifying
the -l flag on the command line
s(x) sine
c(x) cosine
e(x) exponential
l(x) log
a(x) arctangent
j(n,x) Bessel function
All function arguments are passed by value.
The value of a statement that is an expression is printed
unless the main
operator is an assignment. The value printed is assigned to
the special
variable `last'. This is a non-portable extension. A single dot may be
used as a synonym for `last'. Either semicolons or newlines
may separate
statements. Assignment to scale influences the number of
digits to be
retained on arithmetic operations in the manner of dc(1).
Assignments to
ibase or obase set the input and output number radix respectively.
The same letter may be used as an array, a function, and a
simple variable
simultaneously. All variables are global to the program. `Auto'
variables are pushed down during function calls. When using
arrays as
function arguments or defining them as automatic variables,
empty square
brackets must follow the array name.
For example
scale = 20
define e(x){
auto a, b, c, i, s
a = 1
b = 1
s = 1
for(i=1; 1==1; i++){
a = a*x
b = b*i
c = a/b
if(c == 0) return(s)
s = s+c
}
}
defines a function to compute an approximate value of the
exponential
function and
for(i=1; i<=10; i++) e(i)
prints approximate values of the exponential function of the
first ten
integers.
/usr/share/misc/bc.library math library, read when the -l
option is
specified on the command line.
dc(1)
"BC - An Arbitrary Precision Desk-Calculator Language",
/usr/share/doc/usd/06.bc/.
The bc utility is expected to conform to the IEEE Std 1003.2
(``POSIX.2'') specification.
The bc first command appeared in Version 6 AT&T UNIX. A
complete rewrite
of the bc command first appeared in OpenBSD 3.5.
The original version of the bc command was written by Robert
Morris and
Lorinda Cherry. The current version of the bc utility was
written by
Otto Moerbeek.
`Quit' is interpreted when read, not when executed.
Some non-portable extensions, as found in the GNU version of
the bc utility
are not implemented (yet).
August 8, 1991
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