
BC(1) BC(1)
NAME
bc  arbitraryprecision arithmetic language
SYNOPSIS
bc [ c ] [ l ] [ file ... ]
DESCRIPTION
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 l argument stands for the
name of an arbitrary precision math library. The following syntax for bc programs is like
that of C; L means letter az, E means expression, S means statement.
Lexical
comments are enclosed in /* */
newlines end statements
Names
simple variables: L
array elements: L[E]
The words ibase, obase, and scale
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)
function call
Operators
+  * / % ^ (% is remainder; ^ is power)
++ 
== <= >= != < >
= += = *= /= %= ^=
Statements
E
{ S ; ... ; S }
print E
if ( E ) S
while ( E ) S
for ( E ; E ; E ) S
null statement
break
quit
"text"
Function definitions
define L ( L , ... , L ){
auto L , ... , L
S ; ... ; S
return E
}
Functions in
l math library
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 an expression at the top level is printed unless the main operator is an
assignment. Text in quotes, which may include newlines, is also printed. Either semi
colons 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. Automatic variables are pushed down during func
tion calls. In a declaration of an array as a function argument or automatic variable
empty square brackets must follow the array name.
Bc is actually a preprocessor for dc(1), which it invokes automatically, unless the c
(compile only) option is present. In this case the dc input is sent to the standard out
put instead.
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.)
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)
FILES
/sys/lib/bclib mathematical library
SOURCE
/sys/src/cmd/bc.y
SEE ALSO
dc(1), hoc(1)
BUGS
No or operators.
A statement must have all three
A is interpreted when read, not when executed.
BC(1) 
