NAME
dc – desk calculator 
SYNOPSIS
dc [ file ] 
DESCRIPTION
Dc is an arbitrary precision desk calculator. Ordinarily it operates
on decimal integers, but one may specify an input base, output
base, and a number of fractional digits to be maintained. The
overall structure of dc is a stacking (reverse Polish) calculator.
If an argument is given, input is taken from that file until its
end, then from the standard input. The following constructions
are recognized: number
Sx Pop the top of the stack and store into a register named x, where x may be any character. Under operation S register x is treated as a stack and the value is pushed on it. lx Lx Push the value in register x onto the stack. The register x is not altered. All registers start with zero value. Under operation L register x is treated as a stack and its top value is popped onto the main stack. d Duplicate the top value on the stack. p Print the top value on the stack. The top value remains unchanged. P interprets the top of the stack as a text string, removes it, and prints it. f Print the values on the stack. q Q Exit the program. If executing a string, the recursion level is popped by two. Under operation Q the top value on the stack is popped and the string execution level is popped by that value. x Treat the top element of the stack as a character string and execute it as a string of dc commands. X Replace the number on the top of the stack with its scale factor. [ ... ]
>x =x Pop and compare the top two elements of the stack. Register x is executed if they obey the stated relation. v Replace the top element on the stack by its square root. Any existing fractional part of the argument is taken into account, but otherwise the scale factor is ignored. ! Interpret the rest of the line as a shell command. c Clear the stack. i The top value on the stack is popped and used as the number base for further input. I Push the input base on the top of the stack. o The top value on the stack is popped and used as the number base for further output. In bases larger than 10, each `digit' prints as a group of decimal digits. O Push the output base on the top of the stack. k Pop the top of the stack, and use that value as a non–negative scale factor: the appropriate number of places are printed on output, and maintained during multiplication, division, and exponentiation. The interaction of scale factor, input base, and output base will be reasonable if all are changed together. z Push the stack level onto the stack. Z Replace the number on the top of the stack with its length. ? A line of input is taken from the input source (usually the terminal) and executed. ; : Used by bc for array operations.
The scale factor set by k determines how many digits are kept
to the right of the decimal point. If s is the current scale factor,
sa is the scale of the first operand, sb is the scale of the second,
and b is the (integer) second operand, results are truncated to
the following scales.

EXAMPLES
Print the first ten values of n!

SOURCE
/sys/src/cmd/dc.c 
SEE ALSO
bc(1), hoc(1) 
DIAGNOSTICS
x is unimplemented, where x is an octal number: an internal error. `Out of headers' for too many numbers being kept around. `Nesting depth' for too many levels of nested execution. 
BUGS
When the input base exceeds 16, there is no notation for digits
greater than F.
Past its time. 