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<div class="subsection-level-extent" id="Auto_002dincrement">
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<h4 class="subsection" id="Auto_002dincrement-1">5.8.3 Auto-increment</h4>
<a class="index-entry-id" id="index-auto_002dincrementation-of-a-register"></a>
<a class="index-entry-id" id="index-incrementation_002c-automatic_002c-of-a-register"></a>
<a class="index-entry-id" id="index-decrementation_002c-automatic_002c-of-a-register"></a>
<p>Registers can also be incremented or decremented by a configured amount
at the time they are interpolated. The value of the increment is
specified with a third argument to the <code class="code">nr</code> request, and a special
interpolation syntax is used to alter and then retrieve the register’s
value. Together, these features are called
<em class="dfn">auto-increment</em>.<a class="footnote" id="DOCF51" href="groff.html_fot.html#FOOT51"><sup>51</sup></a>
</p>
<dl class="first-deffn">
<dt class="deffn" id="index-_002enr-4"><span class="category-def">Request: </span><span><strong class="def-name"><code class="t">.nr</code></strong> <var class="def-var-arguments">ident value incr</var><a class="copiable-link" href='#index-_002enr-4'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-nr-3"></a>
<a class="index-entry-id" id="index-_005cR_002c-difference-from-nr"></a>
<p>Set register <var class="var">ident</var> to <var class="var">value</var> and its auto-incrementation
amount to to <var class="var">incr</var>. The <code class="code">\R</code> escape sequence doesn’t support
an <var class="var">incr</var> argument.
</p></dd></dl>
<p>Auto-incrementation is not <em class="emph">completely</em> automatic; the <code class="code">\n</code>
escape sequence in its basic form never alters the value of a register.
To apply auto-incrementation to a register, interpolate it with
‘<samp class="samp">\n�</samp>’.
</p>
<dl class="first-deffn">
<dt class="deffn" id="index-_005cn_002bi"><span class="category-def">Escape sequence: </span><span><strong class="def-name"><code class="t">\n+</code><span class="r"><i class="slanted">i</i></span><code class="t"></code></strong><a class="copiable-link" href='#index-_005cn_002bi'> ¶</a></span></dt>
<dd><a class="index-entry-id" id="index-_005cn-1"></a>
</dd><dt class="deffnx def-cmd-deffn" id="index-_005cn_002di"><span class="category-def">Escape sequence: </span><span><strong class="def-name"><code class="t">\n-</code><span class="r"><i class="slanted">i</i></span><code class="t"></code></strong><a class="copiable-link" href='#index-_005cn_002di'> ¶</a></span></dt>
<dt class="deffnx def-cmd-deffn" id="index-_005cn_002b_0028id"><span class="category-def">Escape sequence: </span><span><strong class="def-name"><code class="t">\n+(</code><span class="r"><i class="slanted">id</i></span><code class="t"></code></strong><a class="copiable-link" href='#index-_005cn_002b_0028id'> ¶</a></span></dt>
<dt class="deffnx def-cmd-deffn" id="index-_005cn_002d_0028id"><span class="category-def">Escape sequence: </span><span><strong class="def-name"><code class="t">\n-(</code><span class="r"><i class="slanted">id</i></span><code class="t"></code></strong><a class="copiable-link" href='#index-_005cn_002d_0028id'> ¶</a></span></dt>
<dt class="deffnx def-cmd-deffn" id="index-_005cn_002b_005bident_005d"><span class="category-def">Escape sequence: </span><span><strong class="def-name"><code class="t">\n+[</code><span class="r"><i class="slanted">ident</i></span><code class="t">]</code></strong><a class="copiable-link" href='#index-_005cn_002b_005bident_005d'> ¶</a></span></dt>
<dt class="deffnx def-cmd-deffn" id="index-_005cn_002d_005bident_005d"><span class="category-def">Escape sequence: </span><span><strong class="def-name"><code class="t">\n-[</code><span class="r"><i class="slanted">ident</i></span><code class="t">]</code></strong><a class="copiable-link" href='#index-_005cn_002d_005bident_005d'> ¶</a></span></dt>
<dd><p>Increment or decrement <var class="var">ident</var> (one-character
name <var class="var">i</var>, two-character name <var class="var">id</var>) by the register’s
auto-incrementation value and then interpolate the new register value.
If <var class="var">ident</var> has no auto-incrementation value, interpolate as with
<code class="code">\n</code>.
</p></dd></dl>
<div class="example">
<div class="group"><pre class="example-preformatted">.nr a 0 1
.nr xx 0 5
.nr foo 0 -2
\n+a, \n+a, \n+a, \n+a, \n+a
.br
\n-(xx, \n-(xx, \n-(xx, \n-(xx, \n-(xx
.br
\n+[foo], \n+[foo], \n+[foo], \n+[foo], \n+[foo]
⇒ 1, 2, 3, 4, 5
⇒ -5, -10, -15, -20, -25
⇒ -2, -4, -6, -8, -10
</pre></div></div>
<a class="index-entry-id" id="index-increment-value-without-changing-the-register"></a>
<a class="index-entry-id" id="index-value_002c-incrementing-without-changing-the-register"></a>
<p>To change the increment value without changing the value of a register,
assign the register’s value to itself by interpolating it, and specify
the desired increment normally. Apply an increment of ‘<samp class="samp">0</samp>’ to
disable auto-incrementation of the register.
</p>
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