bc(1)

Name

bc − interactive arithmetic language processor

Syntax

bc [−c] [−l] [file...]

Description

The bc command provides 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. The −l argument stands for the name of an arbitrary precision math library. The syntax for bc programs is as follows: L means letter a-z, E means expression, S means statement.

Comments
are enclosed in /* and */.

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 )

Operators
+ − * / % ^ (% is remainder; ^ is power)
++ −− (prefix and postfix; apply to names)
== <= >= != < >
= += −= *= /= %= ^=

Statements
E
{ S ; ... ; S }
if ( E ) S
while ( E ) S
for ( E ; E ; E ) S
null statement
break
quit

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 a statement that is an expression is printed unless the main operator is an assignment. Either semicolons or new lines may separate statements. Assignment to scale influences the number of digits to be retained on arithmetic operations in the manner of dc(.). 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. ‘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.

The following example defines a function to compute an approximate value of the exponential function:

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
}
}

The following command line then prints approximate values of the exponential function of the first ten integers:

for(i=1; i<=10; i++) e(i)

The bc command is actually a preprocessor for dc(,), 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.

Options

−c Compiles input only.

−l Names arbitrary precision math library.

Restrictions

The for statement must have all three E’s.

Quit is interpreted when read, not when executed.

Variables must be a single lower case letter. Upper case letters are used only as digits for bases greater than 10.

Files

/usr/lib/lib.bmathematical library

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