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<p>Executes a <span class="t-spar">statement</span> repeatedly until the value of <span class="t-spar">condition</span> becomes false. The test takes place after each iteration.
</p>
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<li class="toclevel-1 tocsection-1"><a href="do.html#Syntax"><span class="tocnumber">1</span> <span class="toctext">Syntax</span></a></li>
<li class="toclevel-1 tocsection-2"><a href="do.html#Explanation"><span class="tocnumber">2</span> <span class="toctext">Explanation</span></a></li>
<li class="toclevel-1 tocsection-3"><a href="do.html#Notes"><span class="tocnumber">3</span> <span class="toctext">Notes</span></a></li>
<li class="toclevel-1 tocsection-4"><a href="do.html#Keywords"><span class="tocnumber">4</span> <span class="toctext">Keywords</span></a></li>
<li class="toclevel-1 tocsection-5"><a href="do.html#Example"><span class="tocnumber">5</span> <span class="toctext">Example</span></a></li>
<li class="toclevel-1 tocsection-6"><a href="do.html#References"><span class="tocnumber">6</span> <span class="toctext">References</span></a></li>
<li class="toclevel-1 tocsection-7"><a href="do.html#See_also"><span class="tocnumber">7</span> <span class="toctext">See also</span></a></li>
</ul>
</td></tr></table>
<h3><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=c/language/do&action=edit&section=1" title="Edit section: Syntax">edit</a>]</span> <span class="mw-headline" id="Syntax">Syntax</span></h3>
<table class="t-sdsc-begin">
<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr>
<tr class="t-sdsc">
<td class="t-sdsc-nopad"> <code><b>do</b></code> <span class="t-spar">statement</span> <code><b>while (</b></code> <span class="t-spar">expression</span> <code><b>)</b></code> <code><b>;</b></code>
</td>
<td class="t-sdsc-nopad">
</td>
<td class="t-sdsc-nopad">
</td></tr>
<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr></table>
<table class="t-par-begin">
<tr class="t-par">
<td> <span class="t-spar">expression</span>
</td>
<td> -
</td>
<td> any <a href="expressions.html" title="c/language/expressions">expression</a> of <a href="compatible_type.html#Type_groups" title="c/language/type">scalar type</a>. This expression is evaluated after each iteration, and if it compares equal to zero, the loop is exited.
</td></tr>
<tr class="t-par">
<td> <span class="t-spar">statement</span>
</td>
<td> -
</td>
<td> any <a href="statements.html" title="c/language/statements">statement</a>, typically a compound statement, which is the body of the loop
</td></tr></table>
<h3><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=c/language/do&action=edit&section=2" title="Edit section: Explanation">edit</a>]</span> <span class="mw-headline" id="Explanation">Explanation</span></h3>
<p>A <code>do-while</code> statement causes the <span class="t-spar">statement</span> (also called <i>the loop body</i>) to be executed repeatedly until the <span class="t-spar">expression</span> (also called <i>controlling expression</i>) compares equal to 0. The repetition occurs regardless of whether the loop body is entered normally or by a <a href="goto.html" title="c/language/goto">goto</a> into the middle of <span class="t-spar">statement</span>.
</p><p>The evaluation of <span class="t-spar">expression</span> takes place after each execution of <span class="t-spar">statement</span> (whether entered normally or by a goto). If the controlling expression needs to be evaluated before the loop body, the <a href="while.html" title="c/language/while">while loop</a> or the <a href="for.html" title="c/language/for">for loop</a> may be used.
</p><p>If the execution of the loop needs to be terminated at some point, <a href="break.html" title="c/language/break"> break statement</a> can be used as terminating statement.
</p><p>If the execution of the loop needs to be continued at the end of the loop body, <a href="continue.html" title="c/language/continue"> continue statement</a> can be used as a shortcut.
</p><p>As an extension to the <a href="http://en.cppreference.com/mwiki/index.php?title=c/language/as-if&action=edit&redlink=1" class="new" title="c/language/as-if (page does not exist)">as-if</a> rule, a loop with no side effects (I/O, volatile accesses, or atomic synchronizations) in any part of its <span class="t-spar">expression</span> or <span class="t-spar">loop_statement</span> may be optimized out even if it is an endless loop. The only exceptions are the loops where <span class="t-spar">expression</span> is a constant expression; <code>do {...} while(true);</code> is always an endless loop.
</p>
<table class="t-rev-begin">
<tr class="t-rev t-since-c99"><td>
<p>As with all other selection and iteration statements, the do-while statement establishes <a href="scope.html" title="c/language/scope">block scope</a>: any identifier introduced in the <span class="t-spar">expression</span> goes out of scope after the statement.
</p>
</td>
<td><span class="t-mark-rev t-since-c99">(since C99)</span></td></tr>
</table>
<h3><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=c/language/do&action=edit&section=3" title="Edit section: Notes">edit</a>]</span> <span class="mw-headline" id="Notes">Notes</span></h3>
<p>Boolean and pointer expressions are often used as loop controlling expressions. The boolean value <code>false</code> and the null pointer value of any pointer type compare equal to zero.
</p>
<h3><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=c/language/do&action=edit&section=4" title="Edit section: Keywords">edit</a>]</span> <span class="mw-headline" id="Keywords">Keywords</span></h3>
<p><a href="../keyword/do.html" title="c/keyword/do"><tt>do</tt></a>,
<a href="../keyword/while.html" title="c/keyword/while"><tt>while</tt></a>
</p>
<h3><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=c/language/do&action=edit&section=5" title="Edit section: Example">edit</a>]</span> <span class="mw-headline" id="Example">Example</span></h3>
<div class="t-example"><div class="t-example-live-link"><div class="coliru-btn coliru-btn-run-init">Run this code</div></div>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="co2">#include <stdio.h></span>
<span class="co2">#include <stdlib.h></span>
<span class="kw2">enum</span> <span class="br0">{</span> SIZE <span class="sy1">=</span> <span class="nu0">8</span> <span class="br0">}</span><span class="sy4">;</span>
<span class="kw4">int</span> main<span class="br0">(</span><span class="kw4">void</span><span class="br0">)</span>
<span class="br0">{</span>
<span class="co1">// trivial example</span>
<span class="kw4">int</span> array<span class="br0">[</span>SIZE<span class="br0">]</span>, n <span class="sy1">=</span> <span class="nu0">0</span><span class="sy4">;</span>
<span class="kw1">do</span> array<span class="br0">[</span>n<span class="sy2">++</span><span class="br0">]</span> <span class="sy1">=</span> <a href="../numeric/random/rand.html"><span class="kw741">rand</span></a><span class="br0">(</span><span class="br0">)</span> <span class="sy2">%</span> <span class="nu0">2</span><span class="sy4">;</span> <span class="co1">// the loop body is a single expression statement</span>
<span class="kw1">while</span><span class="br0">(</span>n <span class="sy1"><</span> SIZE<span class="br0">)</span><span class="sy4">;</span>
<a href="../io/puts.html"><span class="kw836">puts</span></a><span class="br0">(</span><span class="st0">"Array filled!"</span><span class="br0">)</span><span class="sy4">;</span>
n <span class="sy1">=</span> <span class="nu0">0</span><span class="sy4">;</span>
<span class="kw1">do</span> <span class="br0">{</span> <span class="co1">// the loop body is a compound statement</span>
<a href="../io/fprintf.html"><span class="kw851">printf</span></a><span class="br0">(</span><span class="st0">"%d "</span>, array<span class="br0">[</span>n<span class="br0">]</span><span class="br0">)</span><span class="sy4">;</span>
<span class="sy2">++</span>n<span class="sy4">;</span>
<span class="br0">}</span> <span class="kw1">while</span> <span class="br0">(</span>n <span class="sy1"><</span> SIZE<span class="br0">)</span><span class="sy4">;</span>
<a href="../io/fprintf.html"><span class="kw851">printf</span></a><span class="br0">(</span><span class="st0">"<span class="es1">\n</span>"</span><span class="br0">)</span><span class="sy4">;</span>
 
<span class="co1">// the loop from K&R itoa(). The do-while loop is used</span>
<span class="co1">// because there is always at least one digit to generate</span>
<span class="kw4">int</span> num <span class="sy1">=</span> <span class="nu0">1234</span>, i<span class="sy1">=</span><span class="nu0">0</span><span class="sy4">;</span>
<span class="kw4">char</span> s<span class="br0">[</span><span class="nu0">10</span><span class="br0">]</span><span class="sy4">;</span>
<span class="kw1">do</span> s<span class="br0">[</span>i<span class="sy2">++</span><span class="br0">]</span> <span class="sy1">=</span> num <span class="sy2">%</span> <span class="nu0">10</span> <span class="sy2">+</span> <span class="st0">'0'</span><span class="sy4">;</span> <span class="co1">// get next digit in reverse order</span>
<span class="kw1">while</span> <span class="br0">(</span><span class="br0">(</span>num <span class="sy2">/</span><span class="sy1">=</span> <span class="nu0">10</span><span class="br0">)</span> <span class="sy1">></span> <span class="nu0">0</span><span class="br0">)</span><span class="sy4">;</span>
s<span class="br0">[</span>i<span class="br0">]</span> <span class="sy1">=</span> <span class="st0">'<span class="es5">\0</span>'</span><span class="sy4">;</span>
<a href="../io/puts.html"><span class="kw836">puts</span></a><span class="br0">(</span>s<span class="br0">)</span><span class="sy4">;</span>
<span class="br0">}</span></pre></div></div>
<p>Possible output:
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="text source-text"><pre class="de1">Array filled!
1 0 1 1 1 1 0 0
4321</pre></div></div>
</div>
<h3><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=c/language/do&action=edit&section=6" title="Edit section: References">edit</a>]</span> <span class="mw-headline" id="References">References</span></h3>
<div class="t-ref-std-11">
<ul><li> C11 standard (ISO/IEC 9899:2011):
</li></ul>
<dl><dd><ul><li> 6.8.5.2 The do statement (p: 151)
</li></ul>
</dd></dl>
<div class="t-ref-std-c99">
<ul><li> C99 standard (ISO/IEC 9899:1999):
</li></ul>
<dl><dd><ul><li> 6.8.5.2 The do statement (p: 136)
</li></ul>
</dd></dl>
<div class="t-ref-std-c89">
<ul><li> C89/C90 standard (ISO/IEC 9899:1990):
</li></ul>
<dl><dd><ul><li> 3.6.5.2 The do statement
</li></ul>
</dd></dl>
</div>
<h3><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=c/language/do&action=edit&section=7" title="Edit section: See also">edit</a>]</span> <span class="mw-headline" id="See_also">See also</span></h3>
<table class="t-dsc-begin">
<tr class="t-dsc">
<td colspan="2"> <div class="t-dsc-see"><span><a href="../../cpp/language/do.html" title="cpp/language/do">C++ documentation</a></span> for <span class="t-dsc-see-tt"><span>do-while loop</span></span></div>
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