NAME
bc – arbitrary–precision arithmetic language

SYNOPSIS
bc [ –cdls ] [ 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 –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 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.

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 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 for statement must have all three Es.

A quit is interpreted when read, not when executed.

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