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pbi-ide/help/BasicStampHelp/Content/LanguageTopics/Commands/DO_LOOP.htm

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<head><title>DO…LOOP</title>
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<h1 class="code">DO…LOOP</h1>
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<p>
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<img src="../../graphics/pgm_icon2px.gif" border="0" alt="BS2px icon" title="BS2px icon" /><span class="code_in_text"> {PBASIC&#160;2.5}</span>
</p>
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<p style="text-align: right;"><a href="../ExampleTopics/DoLoopEx.htm" target="" title="" alt="" class="MCXref_0" xrefformat="{paratext}">DO...LOOP Example</a>
</p>
<p>&#160;</p>
</div>
<p class="clear">&#160;</p>
<p>&#160;</p>
<p class="PlainText">Syntax:</p>
<p class="PlainText"><span class="keyword_in_text">DO </span>{ <span class="keyword_in_text">WHILE</span> | <span class="keyword_in_text">UNTIL</span> <![CDATA[ ]]><i>condition(s)</i> }<br />&#160; &#160; &#160;<i>Statement(s)</i><br />&#160; &#160;<span class="keyword_in_text">LOOP</span> { <span class="keyword_in_text">WHILE</span> | <span class="keyword_in_text">UNTIL</span> <![CDATA[ ]]><i>condition(s)</i> }
</p>
<h2>Function</h2>
<p class="PlainText">Create a repeating loop that executes the program lines between <span class="keyword_in_text">DO</span> and
<span class="keyword_in_text">LOOP</span>, optionally testing before or after the loop statements
</p>
<ul>
<li value="1"><b><i>Condition</i></b> is an optional variable/constant/expression (0 -
65535) which determines whether the loop will run or terminate.</li>
<li value="2"><b><i>Statement</i></b> is any valid PBASIC statement.</li>
</ul>
<h2>Quick Facts<br /></h2>
<table width="100%" cellpadding="4" cellspacing="0" border="1">
<tr>
<td width="26%" align="center" bgcolor="#CFCFCF">&#160;</td>
<td width="64%" align="center" bgcolor="#CFCFCF">BS2 Family</td>
</tr>
<tr>
<td align="center" bgcolor="#CFCFCF">Maximum nested loops</td>
<td align="center">16</td>
</tr>
<tr>
<td align="center" bgcolor="#CFCFCF">WHILE <i>Condition</i> evaluation</td>
<td align="center">Run loop if <i>Condition</i> evaluates as True (1)</td>
</tr>
<tr>
<td align="center" bgcolor="#CFCFCF">UNTIL <i>Condition</i> evaluation</td>
<td align="center">Terminate loop if <i>Condition</i> evaluates as True (1)</td>
</tr>
<tr>
<td align="center" bgcolor="#CFCFCF">Related Commands</td>
<td align="center" colspan="1">
<p colspan="1" align="center"><a href="EXIT.htm" target="" title="" alt="" class="MCXref_0" xrefformat="{paratext}">EXIT</a>, <a href="FOR_NEXT.htm" target="" title="" alt="" class="MCXref_0" xrefformat="{paratext}">FOR…NEXT</a></p>
</td>
</tr>
</table>
<h2>Explanation</h2>
<p class="PlainText"><span class="keyword_in_text">DO...LOOP</span> loops let your program execute a series of instructions
indefinitely, or until a specified condition terminates the loop. The simplest
form is shown here: </p><pre class="BScode" xml:space="preserve">
Error_Message:
DO
DEBUG "Error...", CR
PAUSE 2000
LOOP
</pre>
<p class="PlainText">In this example the error message will be printed on the
<a href="DEBUG.htm" target="" title="" alt="" class="MCXref_0" xrefformat="{paratext}">DEBUG</a> screen every two seconds until the BASIC Stamp is
reset. Simple <span class="keyword_in_text">DO...LOOP</span> loops can be terminated with
<a href="EXIT.htm" class="MCXref_0" xrefformat="{paratext}">EXIT</a>. For example:</p><pre class="BScode" xml:space="preserve">
Error_Message:
DO
DEBUG "Error...", CR
PAUSE 1000
IF (AckPin = 0) THEN EXIT ' wait for user button press
LOOP
GOTO Initialize ' re-initialize system
</pre>
<p class="PlainText">In this case the loop will continue until the pin named AckPin is pulled low,
then the loop will terminate and continue at the line <span class="code_in_text">GOTO Initialize</span>.</p>
<p class="PlainText">More often than not, you will want to test some condition to determine whether
the loop code should run or continue to run. A loop that tests the condition before
running loop code is constructed like this:</p><pre class="BScode" xml:space="preserve">
reps VAR Nib
Print_Stars:
DO WHILE (reps &lt; 3) ' test before loop statements
DEBUG "*"
reps = reps + 1
LOOP
</pre>
<p class="PlainText">In this program the loop code <span class="code_in_text">DEBUG "*"</span> will not run unless the <span class="keyword_in_text">WHILE</span>
condition evaluates as True. Another way to write the loop is like this:</p><pre class="BScode" xml:space="preserve">
reps VAR Nib
Print_Stars:
DO
DEBUG "*"
reps = reps + 1
LOOP UNTIL (reps &gt;= 3) ' test after loop statements
</pre>
<p class="PlainText">The difference is that with this loop, the loop statements will always run at
least once before the condition is tested and will continue to as long as the
<span class="keyword_in_text">UNTIL</span> condition evaluates as False.</p>
<p class="PlainText">Note that <span class="keyword_in_text">WHILE</span> (loop runs while True) and <span class="keyword_in_text">UNTIL</span> (loop runs until
True) tests can be interchanged, but are generally used as illustrated above.
</p>
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<p style="text-align: right;"><span class="ContactInfoProjectName">BASIC Stamp Help</span> <![CDATA[ ]]><span class="ContactInfoVersion#">Version 2.5.4</span> <![CDATA[ ]]></p>
<p style="text-align: right;">Copyright ©&#160;<span class="ContactInfoCompanyName">Parallax Inc.</span></p>
<p style="text-align: right;"><span class="SystemShortDate">8/8/2012</span>
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