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<!-- This manual documents version 1.4.1 of
GNU dc, an arbitrary precision calculator.

Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License,
Version 1.2 or any later version published by the Free Software Foundation;
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<title>dc, an arbitrary precision calculator</title>

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<div class="top-level-extent" id="Top">
<div class="nav-panel">
<p>
Next: <a href="#Introduction" accesskey="n" rel="next">Introduction</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p>
</div>
<h1 class="top" id="GNU-dc"><span>GNU dc<a class="copiable-link" href="#GNU-dc"> &para;</a></span></h1>
<p>This manual documents version 1.4.1 of
<small class="sc">GNU</small> <code class="command">dc</code>, an arbitrary precision calculator.
</p>
<p>Copyright (C) 1984, 1994, 1997, 1998, 2000, 2005, 2006, 2008, 2013, 2016
Free Software Foundation, Inc.
</p>
<blockquote class="quotation">
<p>Permission is granted to copy, distribute and/or modify this document
under the terms of the <small class="sc">GNU</small> Free Documentation License,
Version 1.2 or any later version published by the Free Software Foundation;
with no Invariant Sections, with no Front-Cover Texts,
and with no Back-Cover Texts.
A copy of the license can be found at
<a class="url" href="http://www.gnu.org/licenses/fdl.html">http://www.gnu.org/licenses/fdl.html</a> .
</p></blockquote>

<div class="element-contents" id="SEC_Contents">
<h2 class="contents-heading">Table of Contents</h2>

<ul class="toc-numbered-mark">
  <li><a id="toc-Introduction-1" href="#Introduction">1 Introduction</a></li>
  <li><a id="toc-Invocation-1" href="#Invocation">2 Invocation</a></li>
  <li><a id="toc-Printing-Commands-1" href="#Printing-Commands">3 Printing Commands</a></li>
  <li><a id="toc-Arithmetic-1" href="#Arithmetic">4 Arithmetic</a></li>
  <li><a id="toc-Stack-Control-1" href="#Stack-Control">5 Stack Control</a></li>
  <li><a id="toc-Registers-1" href="#Registers">6 Registers</a></li>
  <li><a id="toc-Parameters-1" href="#Parameters">7 Parameters</a></li>
  <li><a id="toc-Strings-1" href="#Strings">8 Strings</a></li>
  <li><a id="toc-Status-Inquiry-1" href="#Status-Inquiry">9 Status Inquiry</a></li>
  <li><a id="toc-Miscellaneous-1" href="#Miscellaneous">10 Miscellaneous</a></li>
  <li><a id="toc-Reporting-bugs-1" href="#Reporting-bugs">11 Reporting bugs</a></li>
</ul>
</div>
</div>
<hr>
<div class="chapter-level-extent" id="Introduction">
<div class="nav-panel">
<p>
Next: <a href="#Invocation" accesskey="n" rel="next">Invocation</a>, Previous: <a href="#Top" accesskey="p" rel="prev">GNU dc</a>, Up: <a href="#Top" accesskey="u" rel="up">GNU dc</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p>
</div>
<h2 class="chapter" id="Introduction-1"><span>1 Introduction<a class="copiable-link" href="#Introduction-1"> &para;</a></span></h2>

<p><code class="command">dc</code> is a reverse-polish desk calculator
which supports unlimited precision arithmetic.
It also allows you to define and call macros.
Normally <code class="command">dc</code> reads from the standard input;
if any command arguments are given to it, they are filenames,
and <code class="command">dc</code> reads and executes the contents of the files
instead of reading from standard input.
All normal output is to standard output;
all error messages are written to standard error.
</p>
<p>To exit, use &lsquo;<samp class="samp">q</samp>&rsquo;.
<kbd class="kbd">C-c</kbd>
(or whatever other keystroke your system uses to generate a <code class="code">SIGINT</code>)
does not exit;
it is used to abort macros that are looping, etc.
</p>
<p>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.
</p>
<p>To enter a number in <code class="command">dc</code>, type the digits (using upper
case letters <code class="code">A</code> through <code class="code">F</code> as &quot;digits&quot; 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 &lsquo;<samp class="samp">_</samp>&rsquo;.
&lsquo;<samp class="samp">-</samp>&rsquo; 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.
</p>
<hr>
</div>
<div class="chapter-level-extent" id="Invocation">
<div class="nav-panel">
<p>
Next: <a href="#Printing-Commands" accesskey="n" rel="next">Printing Commands</a>, Previous: <a href="#Introduction" accesskey="p" rel="prev">Introduction</a>, Up: <a href="#Top" accesskey="u" rel="up">GNU dc</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p>
</div>
<h2 class="chapter" id="Invocation-1"><span>2 Invocation<a class="copiable-link" href="#Invocation-1"> &para;</a></span></h2>

<p><code class="command">dc</code> may be invoked with the following command-line options:
</p><dl class="table">
<dt>&lsquo;<samp class="samp">-e <var class="var">expr</var></samp>&rsquo;</dt>
<dt>&lsquo;<samp class="samp">--expression=<var class="var">expr</var></samp>&rsquo;</dt>
<dd><p>Evaluate <var class="var">expr</var> as <code class="command">dc</code> commands.
</p>
</dd>
<dt>&lsquo;<samp class="samp">-f <var class="var">file</var></samp>&rsquo;</dt>
<dt>&lsquo;<samp class="samp">--file=<var class="var">file</var></samp>&rsquo;</dt>
<dd><p>Read and evaluate <code class="command">dc</code> commands from <var class="var">file</var>.
</p>
</dd>
<dt>&lsquo;<samp class="samp">-h</samp>&rsquo;</dt>
<dt>&lsquo;<samp class="samp">--help</samp>&rsquo;</dt>
<dd><p>Print a usage message summarizing the command-line options, then exit.
</p>
</dd>
<dt>&lsquo;<samp class="samp">-V</samp>&rsquo;</dt>
<dt>&lsquo;<samp class="samp">--version</samp>&rsquo;</dt>
<dd><p>Print the version information for this program, then exit.
</p></dd>
</dl>

<p>If any command-line parameters remain after processing the options,
these parameters are interpreted as additional <var class="var">file</var>s whose
contents are read and evaluated.
A file name of <code class="code">-</code> refers to the standard input stream.
If no <code class="code">-e</code> option was specified, and no files were specified,
then the standard input will be read for commands to evaluate.
</p>
<hr>
</div>
<div class="chapter-level-extent" id="Printing-Commands">
<div class="nav-panel">
<p>
Next: <a href="#Arithmetic" accesskey="n" rel="next">Arithmetic</a>, Previous: <a href="#Invocation" accesskey="p" rel="prev">Invocation</a>, Up: <a href="#Top" accesskey="u" rel="up">GNU dc</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p>
</div>
<h2 class="chapter" id="Printing-Commands-1"><span>3 Printing Commands<a class="copiable-link" href="#Printing-Commands-1"> &para;</a></span></h2>

<dl class="table">
<dt>&lsquo;<samp class="samp">p</samp>&rsquo;</dt>
<dd><p>Prints the value on the top of the stack,
without altering the stack.
A newline is printed after the value.
</p>
</dd>
<dt>&lsquo;<samp class="samp">n</samp>&rsquo;</dt>
<dd><p>Prints the value on the top of the stack, popping it off,
and does not print a newline after.
(This command is a <small class="sc">GNU</small> extension.)
</p>
</dd>
<dt>&lsquo;<samp class="samp">P</samp>&rsquo;</dt>
<dd><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 &quot;base (UCHAR_MAX+1)&quot; byte stream.
Assuming that (UCHAR_MAX+1) is 256
(as it is on most machines with 8-bit bytes),
the sequence
<code class="code">KSK0k1/ _1Ss[ls*]Sxd0&gt;x
[256~Ssd0&lt;x]dsxx
sx[q]Sq[Lsd0&gt;qaPlxx]dsxx
sx0sqLqsxLxLK+k</code>
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.)
(Details of the behavior with a number are a <small class="sc">GNU</small> extension.
Traditional <code class="command">dc</code> happened to &quot;support&quot; similar functionality
for a limited range of inputs as an accidental side-effect of its
internal representation of numbers.)
</p>
</dd>
<dt>&lsquo;<samp class="samp">f</samp>&rsquo;</dt>
<dd><p>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.
</p></dd>
</dl>

<p>All numeric output is split to fit within 70 columns, by default.
When a number is broken up in this way, the split is indicated
by a &quot;\&quot; at the end of the to-be-continued output lines.
The column width at which output is split can be overridden
by setting the <var class="var">DC_LINE_LENGTH</var> environment variable to
the desired width.
A <var class="var">DC_LINE_LENGTH</var> of 0 (zero) disables the line-split
feature altogether.
Invalid values of <var class="var">DC_LINE_LENGTH</var> are silently ignored.
(The <var class="var">DC_LINE_LENGTH</var> variable is a <small class="sc">GNU</small> extension.)
</p>
<hr>
</div>
<div class="chapter-level-extent" id="Arithmetic">
<div class="nav-panel">
<p>
Next: <a href="#Stack-Control" accesskey="n" rel="next">Stack Control</a>, Previous: <a href="#Printing-Commands" accesskey="p" rel="prev">Printing Commands</a>, Up: <a href="#Top" accesskey="u" rel="up">GNU dc</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p>
</div>
<h2 class="chapter" id="Arithmetic-1"><span>4 Arithmetic<a class="copiable-link" href="#Arithmetic-1"> &para;</a></span></h2>

<dl class="table">
<dt>&lsquo;<samp class="samp">+</samp>&rsquo;</dt>
<dd><p>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.
</p>
</dd>
<dt>&lsquo;<samp class="samp">-</samp>&rsquo;</dt>
<dd><p>Pops two values, subtracts the first one popped
from the second one popped, and pushes the result.
</p>
</dd>
<dt>&lsquo;<samp class="samp">*</samp>&rsquo;</dt>
<dd><p>Pops two values, multiplies them, and pushes the result.
The number of fraction digits in the result is the largest of
the precision value,
the number of fraction digits in the multiplier,
or the number of fraction digits in the multiplicand;
but in no event exceeding the number of digits required for
an exact result.
</p>
</dd>
<dt>&lsquo;<samp class="samp">/</samp>&rsquo;</dt>
<dd><p>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.
</p>
</dd>
<dt>&lsquo;<samp class="samp">%</samp>&rsquo;</dt>
<dd><p>Pops two values,
computes the remainder of the division that
the &lsquo;<samp class="samp">/</samp>&rsquo; command would do,
and pushes that.
The value computed is the same as that computed by
the sequence <code class="code">Sd dld/ Ld*-</code> .
</p>
</dd>
<dt>&lsquo;<samp class="samp">~</samp>&rsquo;</dt>
<dd><p>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 <code class="code">SdSn lnld/ LnLd%</code> could also accomplish
this function, with slightly different error checking.)
(This command is a <small class="sc">GNU</small> extension.)
</p>
</dd>
<dt>&lsquo;<samp class="samp">^</samp>&rsquo;</dt>
<dd><p>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.
</p>
</dd>
<dt>&lsquo;<samp class="samp">|</samp>&rsquo;</dt>
<dd><p>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 the result may not be accurate if the modulus
is not 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 <code class="code">Sm^Lm%</code>,
but, unlike <code class="code">^</code>,
this command will work with arbitrarily large exponents.
(This command is a <small class="sc">GNU</small> extension.)
</p>
</dd>
<dt>&lsquo;<samp class="samp">v</samp>&rsquo;</dt>
<dd><p>Pops one value, computes its square root, and pushes that.
The maximum of the precision value and the precision of the argument
is used to determine the number of fraction digits in the result.
</p></dd>
</dl>

<p>Most arithmetic operations are affected by the <em class="emph">precision value</em>,
which you can set with the &lsquo;<samp class="samp">k</samp>&rsquo; command.
The default precision value is zero,
which means that all arithmetic except for
addition and subtraction produces integer results.
</p>
<hr>
</div>
<div class="chapter-level-extent" id="Stack-Control">
<div class="nav-panel">
<p>
Next: <a href="#Registers" accesskey="n" rel="next">Registers</a>, Previous: <a href="#Arithmetic" accesskey="p" rel="prev">Arithmetic</a>, Up: <a href="#Top" accesskey="u" rel="up">GNU dc</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p>
</div>
<h2 class="chapter" id="Stack-Control-1"><span>5 Stack Control<a class="copiable-link" href="#Stack-Control-1"> &para;</a></span></h2>

<dl class="table">
<dt>&lsquo;<samp class="samp">c</samp>&rsquo;</dt>
<dd><p>Clears the stack, rendering it empty.
</p>
</dd>
<dt>&lsquo;<samp class="samp">d</samp>&rsquo;</dt>
<dd><p>Duplicates the value on the top of the stack,
pushing another copy of it.
Thus, &lsquo;<samp class="samp">4d*p</samp>&rsquo; computes 4 squared and prints it.
</p>
</dd>
<dt>&lsquo;<samp class="samp">r</samp>&rsquo;</dt>
<dd><p>Reverses the order of (swaps) the top two values on the stack.
(This can also be accomplished with the sequence <code class="code">SaSbLaLb</code>.)
(This command is a <small class="sc">GNU</small> extension.)
</p>
</dd>
<dt>&lsquo;<samp class="samp">R</samp>&rsquo;</dt>
<dd><p>Pops the top-of-stack as an integer <var class="var">n</var>.
Cyclically rotates the top <var class="var">n</var> items on the updated stack.
If <var class="var">n</var> is positive,
then the rotation direction will make the topmost
element the second-from top;
if <var class="var">n</var> is negative,
then the rotation will make the topmost element the
<var class="var">n</var>-th element from the top.
If the stack depth is less than <var class="var">n</var>
then the entire stack is rotated (in the appropriate direction),
without any error being reported.
(This command is a <small class="sc">GNU</small> extension.)
</p></dd>
</dl>

<hr>
</div>
<div class="chapter-level-extent" id="Registers">
<div class="nav-panel">
<p>
Next: <a href="#Parameters" accesskey="n" rel="next">Parameters</a>, Previous: <a href="#Stack-Control" accesskey="p" rel="prev">Stack Control</a>, Up: <a href="#Top" accesskey="u" rel="up">GNU dc</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p>
</div>
<h2 class="chapter" id="Registers-1"><span>6 Registers<a class="copiable-link" href="#Registers-1"> &para;</a></span></h2>

<p><code class="command">dc</code> provides at least 256 memory registers<a class="footnote" id="DOCF1" href="#FOOT1"><sup>1</sup></a>,
each named by a single character.
You can store a number in a register and retrieve it later.
</p>
<dl class="table">
<dt>&lsquo;<samp class="samp">s<var class="var">r</var></samp>&rsquo;</dt>
<dd><p>Pop the value off the top of the stack and
store it into register <var class="var">r</var>.
</p>
</dd>
<dt>&lsquo;<samp class="samp">l<var class="var">r</var></samp>&rsquo;</dt>
<dd><p>Copy the value in register <var class="var">r</var>,
and push it onto the stack.
The value <code class="code">0</code> is retrieved if the
register is uninitialized or its stack has become empty.
This does not alter the contents of <var class="var">r</var>.
</p>
<p>Each register also contains its own stack.
The current register value is the top of the register&rsquo;s stack.
</p>
</dd>
<dt>&lsquo;<samp class="samp">S<var class="var">r</var></samp>&rsquo;</dt>
<dd><p>Pop the value off the top of the (main) stack and
push it onto the stack of register <var class="var">r</var>.
The previous value of the register becomes inaccessible.
</p>
</dd>
<dt>&lsquo;<samp class="samp">L<var class="var">r</var></samp>&rsquo;</dt>
<dd><p>Pop the value off the top of register <var class="var">r</var>&rsquo;s stack
and push it onto the main stack.
The previous value in register <var class="var">r</var>&rsquo;s stack, if any,
is now accessible via the &lsquo;<samp class="samp">l<var class="var">r</var></samp>&rsquo; command.
</p></dd>
</dl>

<hr>
</div>
<div class="chapter-level-extent" id="Parameters">
<div class="nav-panel">
<p>
Next: <a href="#Strings" accesskey="n" rel="next">Strings</a>, Previous: <a href="#Registers" accesskey="p" rel="prev">Registers</a>, Up: <a href="#Top" accesskey="u" rel="up">GNU dc</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p>
</div>
<h2 class="chapter" id="Parameters-1"><span>7 Parameters<a class="copiable-link" href="#Parameters-1"> &para;</a></span></h2>

<p><code class="command">dc</code> 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;
<em class="emph">all</em> numbers typed in use this radix.
The output radix is used for printing numbers.
</p>
<p>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.
</p>
<dl class="table">
<dt>&lsquo;<samp class="samp">i</samp>&rsquo;</dt>
<dd><p>Pops the value off the top of the stack
and uses it to set the input radix.
</p>
</dd>
<dt>&lsquo;<samp class="samp">o</samp>&rsquo;</dt>
<dd><p>Pops the value off the top of the stack
and uses it to set the output radix.
</p>
</dd>
<dt>&lsquo;<samp class="samp">k</samp>&rsquo;</dt>
<dd><p>Pops the value off the top of the stack
and uses it to set the precision.
</p>
</dd>
<dt>&lsquo;<samp class="samp">I</samp>&rsquo;</dt>
<dd><p>Pushes the current input radix on the stack.
</p>
</dd>
<dt>&lsquo;<samp class="samp">O</samp>&rsquo;</dt>
<dd><p>Pushes the current output radix on the stack.
</p>
</dd>
<dt>&lsquo;<samp class="samp">K</samp>&rsquo;</dt>
<dd><p>Pushes the current precision on the stack.
</p>
</dd>
</dl>

<hr>
</div>
<div class="chapter-level-extent" id="Strings">
<div class="nav-panel">
<p>
Next: <a href="#Status-Inquiry" accesskey="n" rel="next">Status Inquiry</a>, Previous: <a href="#Parameters" accesskey="p" rel="prev">Parameters</a>, Up: <a href="#Top" accesskey="u" rel="up">GNU dc</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p>
</div>
<h2 class="chapter" id="Strings-1"><span>8 Strings<a class="copiable-link" href="#Strings-1"> &para;</a></span></h2>

<p><code class="command">dc</code> 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 <code class="command">dc</code> commands).
Both registers and the stack can hold strings,
and <code class="command">dc</code> 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 &lsquo;<samp class="samp">p</samp>&rsquo; command can accept either and prints the object
according to its type.
</p>
<dl class="table">
<dt>&lsquo;<samp class="samp">[<var class="var">characters</var>]</samp>&rsquo;</dt>
<dd><p>Makes a string containing <var class="var">characters</var> and pushes it on the stack.
For example, &lsquo;<samp class="samp">[foo]P</samp>&rsquo; prints the characters &lsquo;<samp class="samp">foo</samp>&rsquo;
(with no newline).
Note that all square brackets (&lsquo;<samp class="samp">[</samp>&rsquo;s and &lsquo;<samp class="samp">]</samp>&rsquo;s) must be balanced;
there is no mechanism provided for handling unbalanced square brackets.
</p>
</dd>
<dt>&lsquo;<samp class="samp">a</samp>&rsquo;</dt>
<dd><p>The mnemonic for this is somewhat erroneous: asciify.
The top-of-stack is popped.
If it was a number, then the low-order byte of this number
is converted into a 1-character string
and pushed onto the stack.
Otherwise the top-of-stack was a string,
and the first character of that string is pushed back.
(This command is a <small class="sc">GNU</small> extension.)
</p>
</dd>
<dt>&lsquo;<samp class="samp">x</samp>&rsquo;</dt>
<dd><p>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, &lsquo;<samp class="samp">[1p]x</samp>&rsquo; executes the macro &lsquo;<samp class="samp">1p</samp>&rsquo;,
which pushes 1 on the stack and prints &lsquo;<samp class="samp">1</samp>&rsquo; on a separate line.
</p>
<p>Macros are most often stored in registers;
&lsquo;<samp class="samp">[1p]sa</samp>&rsquo; stores a macro to print &lsquo;<samp class="samp">1</samp>&rsquo; into register &lsquo;<samp class="samp">a</samp>&rsquo;,
and &lsquo;<samp class="samp">lax</samp>&rsquo; invokes the macro.
</p>
</dd>
<dt>&lsquo;<samp class="samp">&gt;<var class="var">r</var></samp>&rsquo;</dt>
<dd><p>Pops two values off the stack and compares them
assuming they are numbers,
executing the contents of register <var class="var">r</var> as a macro
if the original top-of-stack is greater.
Thus, &lsquo;<samp class="samp">1 2&gt;a</samp>&rsquo; will invoke register &lsquo;<samp class="samp">a</samp>&rsquo;&rsquo;s contents
and &lsquo;<samp class="samp">2 1&gt;a</samp>&rsquo; will not.
</p>
</dd>
<dt>&lsquo;<samp class="samp">!&gt;<var class="var">r</var></samp>&rsquo;</dt>
<dd><p>Similar but invokes the macro if the original top-of-stack is not greater
(is less than or equal to) what was the second-to-top.
</p>
</dd>
<dt>&lsquo;<samp class="samp">&lt;<var class="var">r</var></samp>&rsquo;</dt>
<dd><p>Similar but invokes the macro if the original top-of-stack is less.
</p>
</dd>
<dt>&lsquo;<samp class="samp">!&lt;<var class="var">r</var></samp>&rsquo;</dt>
<dd><p>Similar but invokes the macro if the original top-of-stack is not less
(is greater than or equal to) what was the second-to-top.
</p>
</dd>
<dt>&lsquo;<samp class="samp">=<var class="var">r</var></samp>&rsquo;</dt>
<dd><p>Similar but invokes the macro if the two numbers popped are equal.
</p>
</dd>
<dt>&lsquo;<samp class="samp">!=<var class="var">r</var></samp>&rsquo;</dt>
<dd><p>Similar but invokes the macro if the two numbers popped are not equal.
</p>
</dd>
<dt>&lsquo;<samp class="samp">?</samp>&rsquo;</dt>
<dd><p>Reads a line from the terminal and executes it.
This command allows a macro to request input from the user.
</p>
</dd>
<dt>&lsquo;<samp class="samp">q</samp>&rsquo;</dt>
<dd><p>During the execution of a macro,
this command exits from the 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 &lsquo;<samp class="samp">q</samp>&rsquo; command will cause <code class="command">dc</code> to exit.
</p>
</dd>
<dt>&lsquo;<samp class="samp">Q</samp>&rsquo;</dt>
<dd><p>Pops a value off the stack and uses it as a count
of levels of macro execution to be exited.
Thus, &lsquo;<samp class="samp">3Q</samp>&rsquo; exits three levels.
</p></dd>
</dl>

<hr>
</div>
<div class="chapter-level-extent" id="Status-Inquiry">
<div class="nav-panel">
<p>
Next: <a href="#Miscellaneous" accesskey="n" rel="next">Miscellaneous</a>, Previous: <a href="#Strings" accesskey="p" rel="prev">Strings</a>, Up: <a href="#Top" accesskey="u" rel="up">GNU dc</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p>
</div>
<h2 class="chapter" id="Status-Inquiry-1"><span>9 Status Inquiry<a class="copiable-link" href="#Status-Inquiry-1"> &para;</a></span></h2>

<dl class="table">
<dt>&lsquo;<samp class="samp">Z</samp>&rsquo;</dt>
<dd><p>Pops a value off the stack,
calculates the number of decimal digits it has
(or number of characters, if it is a string)
and pushes that number.
</p>
<p>Note that the digit count for a number does
<em class="emph">not</em> include any leading zeros,
even if those appear to the right of the radix point.
This may seem a bit strange at first,
but it is compatible with historical implementations of <code class="command">dc</code>,
and can be argued to be useful for computing the magnitude of a value:
<code class="code">dSaXLaZ-</code> will compute the power-of-ten multiplier
which would be needed to shift the decimal point
to be immediately before the leftmost non-zero digit.
</p>
</dd>
<dt>&lsquo;<samp class="samp">X</samp>&rsquo;</dt>
<dd><p>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.
</p>
</dd>
<dt>&lsquo;<samp class="samp">z</samp>&rsquo;</dt>
<dd><p>Pushes the current stack depth:
the number of objects on the stack
before the execution of the &lsquo;<samp class="samp">z</samp>&rsquo; command.
</p></dd>
</dl>

<hr>
</div>
<div class="chapter-level-extent" id="Miscellaneous">
<div class="nav-panel">
<p>
Next: <a href="#Reporting-bugs" accesskey="n" rel="next">Reporting bugs</a>, Previous: <a href="#Status-Inquiry" accesskey="p" rel="prev">Status Inquiry</a>, Up: <a href="#Top" accesskey="u" rel="up">GNU dc</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p>
</div>
<h2 class="chapter" id="Miscellaneous-1"><span>10 Miscellaneous<a class="copiable-link" href="#Miscellaneous-1"> &para;</a></span></h2>

<dl class="table">
<dt>&lsquo;<samp class="samp">!</samp>&rsquo;</dt>
<dd><p>Will run the rest of the line as a system command.
Note that parsing of the !&lt;, !=, and !&gt; commands take precedence,
so if you want to run a command starting with &lt;, =, or &gt; you will
need to add a space after the !.
</p>
</dd>
<dt>&lsquo;<samp class="samp">#</samp>&rsquo;</dt>
<dd><p>Will interpret the rest of the line as a comment.
(This command is a <small class="sc">GNU</small> extension.)
</p>
</dd>
<dt>&lsquo;<samp class="samp">:<var class="var">r</var></samp>&rsquo;</dt>
<dd><p>Will pop the top two values off of the stack.
The old second-to-top value will be stored in the array <var class="var">r</var>,
indexed by the old top-of-stack value.
</p>
</dd>
<dt>&lsquo;<samp class="samp">;<var class="var">r</var></samp>&rsquo;</dt>
<dd><p>Pops the top-of-stack and uses it as an index into
the array <var class="var">r</var>.
The selected value is then pushed onto the stack.
</p></dd>
</dl>

<p>Note that each stacked instance of a register has its own
array associated with it.
Thus &lsquo;<samp class="samp">1 <var class="var">0:a</var> 0S<var class="var">a</var> 2 <var class="var">0:a</var> L<var class="var">a</var> <var class="var">0;a</var>p</samp>&rsquo;
will print 1, because the 2 was stored in an instance of <var class="var">0:a</var>
that was later popped.
</p>
<hr>
</div>
<div class="chapter-level-extent" id="Reporting-bugs">
<div class="nav-panel">
<p>
Previous: <a href="#Miscellaneous" accesskey="p" rel="prev">Miscellaneous</a>, Up: <a href="#Top" accesskey="u" rel="up">GNU dc</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p>
</div>
<h2 class="chapter" id="Reporting-bugs-1"><span>11 Reporting bugs<a class="copiable-link" href="#Reporting-bugs-1"> &para;</a></span></h2>

<p>Email bug reports to <a class="email" href="mailto:bug-dc@gnu.org">bug-dc@gnu.org</a>.
</p></div>
</div>
<div class="footnotes-segment">
<hr>
<h4 class="footnotes-heading">Footnotes</h4>

<h5 class="footnote-body-heading"><a id="FOOT1" href="#DOCF1">(1)</a></h5>
<p>The
exact number of registers provided by <code class="command">dc</code> depends
on the range of an <code class="code">unsigned char</code> in the C compiler
used to create the <code class="command">dc</code> executable.</p>
</div>

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