NAME

bc − arbitrary-precision arithmetic language

SYNOPSIS

bc [ −c ] [ −l ] [ file ... ]

DESCRIPTION

Bc is an interactive processor for a language that resembles C but provides unlimited precision arithmetic.  It takes input from any files given, then reads the standard input.  The options are as follows:

−c Compile only.  Bc is actually a preprocessor for dc(1), which bc invokes automatically.  Specifying −c prohibits invocation of dc, and sends the dc input to the standard output. 

-l causes an arbitrary precision math library to be pre-defined.  As a side-effect, the scale factor is set. 

The syntax for bc programs is as follows;

L means a letter in the range a−z;
E means expression;
S means statement;
R means relational expression.

Comments
are enclosed in /∗ and ∗/. 

Names
simple variables: L
array elements: L [ E ]
The words “ibase”, “obase”, and “scale”
stacks:~L

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 )
Strings of ASCII characters enclosed in quotes ("). 

Arithmetic operators (yield an E as a result)

+ − ∗ / % ^(% is remainder (not mod, see below); ^ is power)
++  −−(prefix and postfix; apply to names)
= =+ =− =∗ =/ =% =^

Relational operators (yield an R when used as E op E). 
== <= >= != < >

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

Function definitions
define L ( L ,..., L ) {
auto L, ... , L
S; ... S
return ( E )
}

Functions in the −l math library:

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.  No operators are defined for strings, but the string is printed if it appears in a context where an expression result would be printed.  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(1). Assignments to ibase or obase set the input and output number radix respectively, again as defined by dc(1).

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 % operator yields the remainder at the current scale, not the integer modulus.  Thus, at scale 1, 7 % 3 is .1 (one tenth), not 1.  This is because (at scale 1) 7 / 3 is 2.3 with .1 as the remainder. 

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. 

FILES

SEE ALSO

bs(1), dc(1). 

BUGS

There are currently no && (AND) or || (OR) comparisons. 
The for statement must have all three expressions. 
Quit is interpreted when read, not when executed. 
Bc’s parser is not robust in the face of input errors. Some simple expression like 2+2 will tend to get it back into phase.

Hewlett-Packard Company  —  Version B.1,  May 11, 2021