BC(1) — UNIX Programmer’s Manual

NAME

bc − arbitrary-precision arithmetic language

SYNOPSIS

bc [ −c ] [ −l ] [ file ... ]

DESCRIPTION

Bc 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. 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 newlines may separate statements. Assignment to scale influences the number of digits to be retained on arithmetic operations in the manner of dc(1). Scale is initially 0, except when −l is used to read in the default library, whereupon it is set to 20. 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.

For example

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
}
}

defines a function to compute an approximate value of the exponential function and

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

prints approximate values of the exponential function of the first ten integers.

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.

FILES

/usr/lib/lib.bmathematical library
dc(1)desk calculator proper

BUGS

No &&, ||, or ! operators.

For statement must have all three E’s.

Quit is interpreted when read, not when executed.

The library functions perform manipulations on the scale variable to enhance the speed of convergance and accuracy of the final result. It is possible with large parameters to get the message:

scale too big

meaning that the library tried to set a scale value >99. The net effect of this is that the function will be evaluated at a severely reduced precision. Aborting a library function with control-C can cause the variable scale to be left with a different value to that set by the user. For further information, those with a mathematical inclination should examine the library file /usr/lib/lib.b.

7th Edition — Revision 1.3 of 24/11/88

Museum