# dc

##

an arbitrary precision calculator

## Synopsis

dc [-V]
[--version] [-h] [--help]

[-e scriptexpression] [--expression=scriptexpression]

[-f scriptfile] [--file=scriptfile]

[file ...]

## add an example, a script, a trick and tips

## examples

no example yet ...

... Feel free to **add your own example above** to help other Linux-lovers !

## description

*dc* is a
reverse-polish desk calculator which supports unlimited
precision arithmetic. It also allows you to define and call
macros. Normally *dc* reads from the standard input; if
any command arguments are given to it, they are filenames,
and *dc* reads and executes the contents of the files
before reading from standard input. All normal output is to
standard output; all error output is to standard error.

A
reverse-polish calculator stores numbers on a stack.
Entering a number pushes it on the stack. Arithmetic
operations pop arguments off the stack and push the
results.

To enter a
number in *dc*, type the digits (using upper case
letters *A* through *F* as "digits" when
working with input bases greater than ten), with an optional
decimal point. Exponential notation is not supported. To
enter a negative number, begin the number with
’’_’’. ’’-’’
cannot be used for this, as it is a binary operator for
subtraction instead. To enter two numbers in succession,
separate them with spaces or newlines. These have no meaning
as commands.

## options

*dc* may
be invoked with the following command-line options:

**-V**

**--version**

Print out the version of
*dc* that is being run and a copyright notice, then
exit.

**-h**

**--help**

Print a usage message briefly summarizing these
command-line options and the bug-reporting address, then
exit.

**-e** *script*

--expression=*script*

Add the commands in
*script* to the set of commands to be run while
processing the input.

**-f** *script-file*

--file=*script-file*

Add the commands contained in
the file *script-file* to the set of commands to be run
while processing the input.

If any
command-line parameters remain after processing the above,
these parameters are interpreted as the names of input files
to be processed. A file name of **-** refers to the
standard input stream. The standard input will processed if
no script files or expressions are specified.

## arithmetic

**+**

Pops two values off the stack, adds them, and pushes the result.
The precision of the result is determined only by the values of
the arguments, and is enough to be exact.

**-**

Pops two values, subtracts the first one popped from the second
one popped, and pushes the result.

*****

Pops two values, multiplies them, and pushes the result. The
number of fraction digits in the result depends on the current
precision value and the number of fraction digits in the two
arguments.

**/**

Pops two values, divides the second one popped from the first one
popped, and pushes the result. The number of fraction digits is
specified by the precision value.

**%**

Pops two values, computes the remainder of the division that the
**/** command would do, and pushes that. The value computed is
the same as that computed by the sequence **Sd dld/ Ld*-** .

**~**

Pops two values, divides the second one popped from the first one
popped. The quotient is pushed first, and the remainder is pushed
next. The number of fraction digits used in the division is
specified by the precision value. (The sequence **SdSn lnld/
LnLd%** could also accomplish this function, with slightly
different error checking.)

**^**

Pops two values and exponentiates, using the first value popped
as the exponent and the second popped as the base. The fraction
part of the exponent is ignored. The precision value specifies
the number of fraction digits in the result.

**|**

Pops three values and computes a modular exponentiation. The
first value popped is used as the reduction modulus; this value
must be a non-zero number, and should be an integer. The second
popped is used as the exponent; this value must be a non-negative
number, and any fractional part of this exponent will be ignored.
The third value popped is the base which gets exponentiated,
which should be an integer. For small integers this is like the
sequence **Sm^Lm%**, but, unlike **^**, this command will
work with arbitrarily large exponents.

**v**

Pops one value, computes its square root, and pushes that. The
precision value specifies the number of fraction digits in the
result.

Most arithmetic operations are affected by the
’’precision value’’, which you can set
with the **k** command. The default precision value is zero,
which means that all arithmetic except for addition and
subtraction produces integer results.

## miscellaneous

**!**

Will run the rest of the line as a system command. Note that
parsing of the !<, !=, and !> commands take precedence, so
if you want to run a command starting with <, =, or > you
will need to add a space after the !.

**#**

Will interpret the rest of the line as a comment.

**:***r*

Will pop the top two values off of the stack. The old
second-to-top value will be stored in the array *r*, indexed
by the old top-of-stack value.

**;***r*

Pops the top-of-stack and uses it as an index into the array
*r*. The selected value is then pushed onto the stack.

Note that each stacked instance of a register has its own array
associated with it. Thus **1 0:a 0Sa 2 0:a La 0;ap** will
print 1, because the 2 was stored in an instance of 0:a that was
later popped.

## parameters

*dc* has three parameters that control its operation: the
precision, the input radix, and the output radix. The precision
specifies the number of fraction digits to keep in the result of
most arithmetic operations. The input radix controls the
interpretation of numbers typed in; all numbers typed in use this
radix. The output radix is used for printing numbers.

The input and output radices are separate parameters; you can
make them unequal, which can be useful or confusing. The input
radix must be between 2 and 16 inclusive. The output radix must
be at least 2. The precision must be zero or greater. The
precision is always measured in decimal digits, regardless of the
current input or output radix.

**i**

Pops the value off the top of the stack and uses it to set the
input radix.

**o**

Pops the value off the top of the stack and uses it to set the
output radix.

**k**

Pops the value off the top of the stack and uses it to set the
precision.

**I**

Pushes the current input radix on the stack.

**O**

Pushes the current output radix on the stack.

**K**

Pushes the current precision on the stack.

## printing commands

**p**

Prints the value on the top of the stack, without altering the
stack. A newline is printed after the value.

**n**

Prints the value on the top of the stack, popping it off, and
does not print a newline after.

**P**

Pops off the value on top of the stack. If it it a string, it is
simply printed without a trailing newline. Otherwise it is a
number, and the integer portion of its absolute value is printed
out as a "base (UCHAR_MAX+1)" byte stream. Assuming that
(UCHAR_MAX+1) is 256 (as it is on most machines with 8-bit
bytes), the sequence **KSK0k1/_1Ss [ls*]Sxd0>x
[256~Ssd0<x]dsxxsx[q]Sq[Lsd0>qaPlxx]
dsxxsx0sqLqsxLxLK+k** could also accomplish this function.
(Much of the complexity of the above native-dc code is due to the
~ computing the characters backwards, and the desire to ensure
that all registers wind up back in their original states.)

**f**

Prints the entire contents of the stack without altering
anything. This is a good command to use if you are lost or want
to figure out what the effect of some command has been.

## registers

*dc* provides at least 256 memory registers, each named by a
single character. You can store a number or a string in a
register and retrieve it later.

**s***r*

Pop the value off the top of the stack and store it into register
*r*.

**l***r*

Copy the value in register *r* and push it onto the stack.
This does not alter the contents of *r*.

Each register also contains its own stack. The current register
value is the top of the register’s stack.

**S***r*

Pop the value off the top of the (main) stack and push it onto
the stack of register *r*. The previous value of the
register becomes inaccessible.

**L***r*

Pop the value off the top of register *r*’s stack and
push it onto the main stack. The previous value in register
*r*’s stack, if any, is now accessible via the
**l***r* command.

## stack control

**c**

Clears the stack, rendering it empty.

**d**

Duplicates the value on the top of the stack, pushing another
copy of it. Thus, ’’4d*p’’ computes 4
squared and prints it.

**r**

Reverses the order of (swaps) the top two values on the stack.
(This can also be accomplished with the sequence
**SaSbLaLb**.)

## status inquiry

**Z**

Pops a value off the stack, calculates the number of digits it
has (or number of characters, if it is a string) and pushes that
number. The digit count for a number does *not* include any
leading zeros, even if those appear to the right of the radix
point.

**X**

Pops a value off the stack, calculates the number of fraction
digits it has, and pushes that number. For a string, the value
pushed is 0.

**z**

Pushes the current stack depth: the number of objects on the
stack before the execution of the **z** command.

## strings

*dc* has a limited ability to operate on strings as well as
on numbers; the only things you can do with strings are print
them and execute them as macros (which means that the contents of
the string are processed as *dc* commands). All registers
and the stack can hold strings, and *dc* always knows
whether any given object is a string or a number. Some commands
such as arithmetic operations demand numbers as arguments and
print errors if given strings. Other commands can accept either a
number or a string; for example, the **p** command can accept
either and prints the object according to its type.

[*characters***]**

Makes a string containing *characters* (contained between
balanced **[** and **]** characters), and pushes it on the
stack. For example, **[foo]P** prints the characters
**foo** (with no newline).

**a**

The top-of-stack is popped. If it was a number, then the
low-order byte of this number is converted into a string and
pushed onto the stack. Otherwise the top-of-stack was a string,
and the first character of that string is pushed back.

**x**

Pops a value off the stack and executes it as a macro. Normally
it should be a string; if it is a number, it is simply pushed
back onto the stack. For example, **[1p]x** executes the macro
**1p** which pushes **1** on the stack and prints **1**
on a separate line.

Macros are most often stored in registers; **[1p]sa** stores a
macro to print **1** into register **a**, and **lax**
invokes this macro.

**>***r*

Pops two values off the stack and compares them assuming they are
numbers, executing the contents of register *r* as a macro
if the original top-of-stack is greater. Thus, **1 2>a**
will invoke register **a**’s contents and **2
1>a** will not.

**!>***r*

Similar but invokes the macro if the original top-of-stack is not
greater than (less than or equal to) what was the second-to-top.

**<***r*

Similar but invokes the macro if the original top-of-stack is
less.

**!<***r*

Similar but invokes the macro if the original top-of-stack is not
less than (greater than or equal to) what was the second-to-top.

**=***r*

Similar but invokes the macro if the two numbers popped are
equal.

**!=***r*

Similar but invokes the macro if the two numbers popped are not
equal.

**?**

Reads a line from the terminal and executes it. This command
allows a macro to request input from the user.

**q**

exits from a macro and also from the macro which invoked it. If
called from the top level, or from a macro which was called
directly from the top level, the **q** command will cause
*dc* to exit.

**Q**

Pops a value off the stack and uses it as a count of levels of
macro execution to be exited. Thus, **3Q** exits three levels.
The **Q** command will never cause *dc* to exit.

*bugs*
Email bug
reports to **bug-dc[:at:]gnu[:dot:]org**.