term% cat index.txt BC(1) General Commands Manual BC(1)
NAME
bc - arbitrary-precision arithmetic language
SYNOPSIS
bc [ -cdls ] [ file ... ]
DESCRIPTION
Bc is an interactive processor for a language that resembles C but pro‐
vides 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 -d option enables debugging output. The -l option stands for the
name of an arbitrary precision math library. The -s option suppresses
the automatic display of calculation results; all output is via the
print command.
The following syntax for bc programs is like that of C; L means letter
a-z, 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 or the -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 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 vari‐
able simultaneously. All variables are global to the program. Auto‐
matic variables are pushed down during function calls. In a declara‐
tion 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 automati‐
cally, unless the -c (compile only) option is present. In this case
the dc input is sent to the standard output 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)