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Allow the expressions in for (E ; E ; E ) to be empty.

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.\"	@(#)bc.1	6.8 (Berkeley) 8/8/91
.\"
.Dd August 8, 1991
.Dt BC 1
.Sh NAME
.Nm bc
.Nd arbitrary-precision arithmetic language and calculator
.Sh SYNOPSIS
.Nm bc
.Op Fl cl
.Op Ar file ...
.Sh DESCRIPTION
.Nm
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.
.Pp
Options available:
.Bl -tag -width Ds
.It Fl c
.Nm
is actually a preprocessor for
.Xr dc 1 ,
which it invokes automatically, unless the
.Fl c
.Pq compile only
option is present.
In this case the generated
.Xr dc 1
instructions are sent to the standard output,
instead of being interpreted by a running
.Xr dc 1
process.
.It Fl l
Allow specification
of an arbitrary precision math library.
.El
.Pp
The syntax for
.Nm
programs is as follows:
.Sq L
means letter a-z;
.Sq E
means expression;
.Sq S
means statement.
.Pp
Comments
.Bd -unfilled -offset indent -compact
are enclosed in /* and */
.Ed
.Pp
Names
.Bd -unfilled -offset indent -compact
simple variables: L
array elements: L [ E ]
The words `ibase', `obase', and `scale'
.Ed
.Pp
Other operands
.Bd -unfilled -offset indent -compact
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 )
.Ed
.Pp
Operators
.Bd -unfilled -offset indent -compact
+  \-  *  /  %  ^ (`%' is remainder; `^' is power)
++   \-\-         (prefix and postfix; apply to names)
==  <=  >=  !=  <  >
=  +=  \-=  *=  /=  %=  ^=
.Ed
.Pp
Statements
.Bd -unfilled -offset indent -compact
E
{ S ; ... ; S }
if ( E ) S
while ( E ) S
for ( E ; E ; E ) S
null statement
break
continue
quit
a string of characters, enclosed in double quotes
.Ed
.Pp
The E's in a for statement may all three be empty.
This is a non-portable extension.
The continue statement also is a non-portable extension.
.Pp
Function definitions
.Bd -unfilled -offset indent -compact
define L ( L ,..., L ) {
	auto L, ... , L
	S; ... S
	return ( E )
}
.Ed
.Pp
The sequence
.Sq \e\<newline><whitespace>
is ignored within numbers.
A string may contain any character, except double quote.
.Pp
Functions in
.Fl lm
math library
.Bl -tag -width j(n,x) -offset indent -compact
.It s(x)
sine
.It c(x)
cosine
.It e(x)
exponential
.It l(x)
log
.It a(x)
arctangent
.It j(n,x)
Bessel function
.El
.Pp
All function arguments are passed by value.
.Pp
The value of a statement that is an expression is printed
unless the main operator is an assignment.
Either semicolons or newlines may separate statements.
Assignment to
.Ar scale
influences the number of digits to be retained on arithmetic
operations in the manner of
.Xr dc 1 .
Assignments to
.Ar ibase
or
.Ar 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.
`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.
.Pp
For example
.Bd -literal -offset indent
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
	}
}
.Ed
.Pp
defines a function to compute an approximate value of
the exponential function and
.Pp
.Dl for(i=1; i<=10; i++) e(i)
.Pp
prints approximate values of the exponential function of
the first ten integers.
.Sh SEE ALSO
.Xr dc 1
.Rs
.%A L. L. Cherry
.%A R. Morris
.%T "BC \- An arbitrary precision desk-calculator language"
.Re
.Sh STANDARDS
The
.Nm
utility is expected to conform to the
.St -p1003.2
specification.
.Sh HISTORY
The
.Nm
command appeared in
.At v6 .
.Sh BUGS
No
.Sq && ,
.Sq \(or\(or ,
or
.Sq \&!
operators.
.Pp
.Pp
.Ql Quit
is interpreted when read, not when executed.
.Pp
Some non-portable extensions, as found in the GNU version of the
.Nm
utility are not implemented (yet).