.TH DC 1
.SH NAME
dc \- desk calculator
.SH SYNOPSIS
.B dc
[
.I file
]
.SH DESCRIPTION
.I 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
.I 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:
.TP
number
The value of the number is pushed on the stack.
A number is an unbroken string of the digits 
.B 0-9A-F 
or
.BR 0-9a-f .
A hexadecimal number beginning with a lower case
letter must be preceded by a zero to distinguish it
from the command associated with the letter.
It may be preceded by an underscore
.B _
to input a
negative number.
Numbers may contain decimal points.
.TP
.L
+  - /  *  %  ^
Add
.LR + ,
subtract
.LR - ,
multiply
.LR * ,
divide
.LR / ,
remainder
.LR % ,
or exponentiate
.L ^
the top two values on the stack.
The two entries are popped off the stack;
the result is pushed on the stack in their place.
Any fractional part of an exponent is ignored.
.TP
.BI s x
.br
.ns
.TP
.BI S x
Pop the top of the stack and store into
a register named
.IR x ,
where
.I x
may be any character.
Under operation
.B S
register
.I x
is treated as a stack and the value is pushed on it.
.TP
.BI l x
.br
.ns
.TP
.BI L x
Push the value in register
.I x
onto the stack.
The register
.I x
is not altered.
All registers start with zero value.
Under operation
.B L
register
.I x
is treated as a stack and its top value is popped onto the main stack.
.TP
.B  d
Duplicate the
top value on the stack.
.TP
.B  p
Print the top value on the stack.
The top value remains unchanged.
.B P
interprets the top of the stack as an
text
string,
removes it, and prints it.
.TP
.B  f
Print the values on the stack.
.TP
.B  q
.br
.ns
.TP
.B Q
Exit the program.
If executing a string, the recursion level is
popped by two.
Under operation
.B Q
the top value on the stack is popped and the string execution level is popped
by that value.
.TP
.B  x
Treat the top element of the stack as a character string
and execute it as a string of
.I dc
commands.
.TP
.B  X
Replace the number on the top of the stack with its scale factor.
.TP
.B "[ ... ]"
Put the bracketed
text
string on the top of the stack.
.TP
.PD0
.BI < x
.TP
.BI > x
.TP
.BI = x
.PD
Pop and compare the
top two elements of the stack.
Register
.I x
is executed if they obey the stated
relation.
.TP
.B  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.
.TP
.B  !
Interpret the rest of the line as a shell command.
.TP
.B  c
Clear the stack.
.TP
.B  i
The top value on the stack is popped and used as the
number base for further input.
.TP
.B I
Push the input base on the top of the stack.
.TP
.B  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.
.TP
.B O
Push the output base on the top of the stack.
.TP
.B  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.
.TP
.B  z
Push the stack level onto the stack.
.TP
.B  Z
Replace the number on the top of the stack with its length.
.TP
.B  ?
A line of input is taken from the input source (usually the terminal)
and executed.
.TP
.B "; :"
Used by 
.I bc
for array operations.
.PP
The scale factor set by
.B k
determines how many digits are kept to the right of
the decimal point.
If
.I s
is the current scale factor,
.I sa
is the scale of the first operand,
.I sb
is the scale of the second,
and
.I b
is the (integer) second operand,
results are truncated to the following scales.
.IP
.nf
\fL+\fR,\fL-\fR	max(\fIsa,sb\fR)
\fL*\fR	min(\fIsa\fR+\fIsb \fR, max\fR(\fIs,sa,sb\fR))
\fL/\fI	s
\fL%\fR	so that dividend = divisor*quotient + remainder; remainder has sign of dividend
\fL^\fR	min(\fIsa\fR\(mu|\fIb\fR|, max(\fIs,sa\fR))
\fLv\fR	max(\fIs,sa\fR)
.fi
.SH EXAMPLES
.LP
Print the first ten values of
.IR n !
.IP
.EX
[la1+dsa*pla10>y]sy
0sa1
lyx
.EE
.SH SOURCE
.B /sys/src/cmd/dc.c
.SH "SEE ALSO"
.IR bc (1),
.IR hoc (1)
.SH DIAGNOSTICS
.I x
.LR "is unimplemented" ,
where
.I x
is an octal number: an internal error.
.br
`Out of headers'
for too many numbers being kept around.
.br
`Nesting depth'
for too many levels of nested execution.
.SH BUGS
When the input base exceeds 16,
there is no notation for digits greater than
.BR F .
.PP
Past its time.