.TH BC 1 
.SH NAME
bc \- arbitrary-precision arithmetic language
.SH SYNOPSIS
.B bc
[
.B -c
]
[
.B -l
]
[
.B -s
]
[
.I file ...
]
.SH DESCRIPTION
.I Bc
is an interactive processor for a language that resembles
C but provides arithmetic on numbers of arbitrary length with up
to 100 digits right of the decimal point.
It takes input from any files given, then reads
the standard input.
The
.B -l
argument stands for the name
of an arbitrary precision math library.
The
.B -s
argument suppresses the automatic display
of calculation results; all output is via the
.B print
command.
.PP
The following syntax for 
.I bc
programs is like that of C;
.I L
means letter
.BR a - z ,
.I E
means expression,
.I S
means statement.
.TF length(E)
.TP
Lexical
.RS
.HP
comments are enclosed in
.B /* */
.HP
newlines end statements
.RE
.TP
Names
.IP
simple variables:
.I L
.br
array elements:
.IB L [ E ]
.br
The words
.BR ibase ,
.BR obase ,
and
.B scale
.TP
Other operands
.IP
arbitrarily long numbers with optional sign and decimal point.
.RS
.TP
.BI ( E )
.TP
.BI sqrt( E )
.TP
.BI length( E )
number of significant decimal digits
.TP
.BI scale( E )
number of digits right of decimal point
.TP
.IB L ( E , ... ,\fIE\fP)
function call
.RE
.TP
Operators
.RS
.HP
.B "+  -  *  /  %  ^\ "
.RB ( %
is remainder;
.B ^
is power)
.HP
.B "++  --\ "
.TP
.B "==  <=  >=  !=  <  >"
.TP
.B "=  +=  -=  *=  /=  %=  ^="
.RE
.TP
Statements
.RS
.br
.I E
.br
.B {
.I S
.B ;
\&...
.B ;
.I S
.B }
.br
.B "print"
.I E
.br
.B "if ("
.I E
.B )
.I S
.br
.B "while ("
.I E
.B )
.I S
.br
.B "for ("
.I E
.B ;
.I E
.B ;
.I E
.B ")"
.I  S
.br
null statement
.br
.B break
.br
.B quit
.br
\fL"\fRtext\fL"\fR
.RE
.TP
Function definitions
.RS
.br
.B define
.I L
.B (
.I L
.B ,
\&...
.B ,
.I L
.B ){
.PD0
.br
.B auto
.I L
.B ,
\&...
.B ,
.I L
.br
.I S
.B ;
\&...
.B ;
.I  S
.br
.B return
.I E
.LP
.B }
.RE
.TP
Functions in 
.B -l
math library
.RS
.TP
.BI s( x )
sine
.TP
.BI c( x )
cosine
.TP
.BI e( x )
exponential
.TP
.BI l( x )
log
.TP
.BI a( x )
arctangent
.TP
.BI j( "n, x" )
Bessel function
.RE
.PP
.DT
All function arguments are passed by value.
.PD
.PP
The value of an expression at the top level is printed
unless the main operator is an assignment or the
.B -s
command line argument is given.
Text in quotes, which may include newlines, is always printed.
Either semicolons or newlines may separate statements.
Assignment to
.B scale
influences the number of digits to be retained on arithmetic
operations in the manner of
.IR dc (1).
Assignments to
.B ibase
or
.B obase
set the input and output number radix respectively.
.PP
The same letter may be used as an array, a function,
and a simple variable simultaneously.
All variables are global to the program.
Automatic variables are pushed down during function calls.
In a declaration of an array as a function argument
or automatic variable
empty square brackets must follow the array name.
.PP
.I Bc
is actually a preprocessor for
.IR dc (1),
which it invokes automatically, unless the
.B -c
(compile only)
option is present.
In this case the
.I dc
input is sent to the standard output instead.
.SH EXAMPLE
Define a function to compute an approximate value of
the exponential.
Use it to print 10 values.
(The exponential function in the library gives better answers.)
.PP
.EX
scale = 20
define e(x) {
	auto a, b, c, i, s
	a = 1
	b = 1
	s = 1
	for(i=1; 1; i++) {
		a *= x
		b *= i
		c = a/b
		if(c == 0) return s
		s += c
	}
}
for(i=1; i<=10; i++) print e(i)
.EE
.SH FILES
.B /sys/lib/bclib
mathematical library
.SH SOURCE
.B /sys/src/cmd/bc.y
.SH "SEE ALSO"
.IR dc (1), 
.IR hoc (1)
.SH BUGS
No
.LR && ,
.LR || ,
or
.L !
operators.
.br
A
.L for
statement must have all three
.LR E s.
.br
A
.L quit
is interpreted when read, not when executed.