181 lines
10 KiB
HTML
181 lines
10 KiB
HTML
<?xml version="1.0" encoding="utf-8"?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
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<html xmlns:MadCap="http://www.madcapsoftware.com/Schemas/MadCap.xsd" MadCap:lastBlockDepth="6" MadCap:lastHeight="94" MadCap:lastWidth="853" MadCap:disableMasterStylesheet="true" MadCap:tocPath="" MadCap:InPreviewMode="false" MadCap:PreloadImages="false" MadCap:RuntimeFileType="Topic" MadCap:TargetType="WebHelp" lang="en-us" xml:lang="en-us" MadCap:PathToHelpSystem="../../../" MadCap:HelpSystemFileName="Default.xml" MadCap:SearchType="Stem">
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<head><title>IF…THEN…ELSE</title>
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<body>
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<h1 class="code">IF…THEN…ELSE</h1>
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<div class="ImagePlusCaption">
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<div class="Col2">
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<p>
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<img src="../../graphics/pgm_icon2.gif" border="0" alt="BS2 icon" title="BS2 icon" />
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<img src="../../graphics/pgm_icon2e.gif" border="0" alt="BS2e icon" title="BS2e icon" />
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<img src="../../graphics/pgm_icon2sx.gif" border="0" alt="BS2sx icon" title="BS2sx icon" />
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<img src="../../graphics/pgm_icon2px.gif" border="0" alt="BS2px icon" title="BS2px icon" /><span class="code_in_text"> {PBASIC 2.5}</span>
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</p>
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</div>
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<p style="text-align: right;"><a href="../ExampleTopics/IfThenElseEx.htm" target="" title="" alt="" class="MCXref_0" xrefformat="{paratext}">IF...THEN...ELSE Example</a>
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</p>
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<p> </p>
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</div>
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<p class="clear"> </p>
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<p> </p>
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<p class="PlainText">Syntax: <br /><br />   <b>IF</b> <![CDATA[ ]]><i>Condition</i> <![CDATA[ ]]><span class="keyword_in_text">THEN</span><br />     <i>Statement(s)</i><br /> { <span class="keyword_in_text">ELSEIF</span> <![CDATA[ ]]><i>Condition(s)</i> <![CDATA[ ]]><span class="keyword_in_text">THEN</span><br />     <i>Statement(s)</i> }<br /> { <span class="keyword_in_text">ELSE</span><br />     <i>Statement(s)</i> }<br />   <span class="keyword_in_text">ENDIF</span><br /><br />   <b>IF</b> <![CDATA[ ]]><i>Condition</i> <![CDATA[ ]]><span class="keyword_in_text">THEN</span> <![CDATA[ ]]><i>Statement(s)</i>{ <span class="keyword_in_text">ELSEIF</span> <![CDATA[ ]]><i>Statement(s)</i> } { <span class="keyword_in_text">ELSE</span> <![CDATA[ ]]><i>Statement(s)</i> }</p>
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<h2>Function</h2>
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<p class="PlainText">Evaluate <i>Condition</i> and, if it is true, execute the statement(s) following
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<span class="keyword_in_text">THEN</span>, otherwise jump to and evaluate the <span class="keyword_in_text">ELSEIF</span> condition. If no
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<span class="keyword_in_text">ELSEIF</span> statement/block is provided, jump to and execute the statements that
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follow <span class="keyword_in_text">ELSE</span>. If no <span class="keyword_in_text">ELSE</span> block is provided, the program will continue
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at the line that follows <span class="keyword_in_text">ENDIF</span> (or the next line when single-line syntax
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is used).
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</p>
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<ul>
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<li value="1"><b><i>Condition</i></b> is a statement, such as "x = 7" that can be evaluated
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as True or False. The <i>Condition</i> can be a very simple or very complex
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relationship, as described below.</li>
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<li value="2"><b><i>Statement</i></b> is any valid PBASIC statement. Multiple statements
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may be placed on the same line (though not recommended) by separating each
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statement with a colon ( : ).</li>
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</ul>
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<h2>Quick Facts</h2>
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<table width="100%" cellpadding="4" cellspacing="0" border="1">
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<tr>
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<td width="20%" align="center" bgcolor="#CFCFCF"> </td>
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<td width="80%" align="center" bgcolor="#CFCFCF">BS2 Family</td>
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</tr>
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<tr>
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<td align="center" bgcolor="#CFCFCF">Comparison operators</td>
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<td align="center">=, <>, >, <, >=, <=</td>
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</tr>
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<tr>
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<td align="center" bgcolor="#CFCFCF">Conditional Logic Operators</td>
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<td align="center">NOT, AND, OR, XOR</td>
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</tr>
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<tr>
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<td align="center" bgcolor="#CFCFCF">Format of condition</td>
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<td align="center"><i>Value1 Comparison Value2</i>;<br />where <i>Value1</i> and <i>Value2</i> can
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be any of variable, constant or expression</td>
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</tr>
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<tr>
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<td align="center" bgcolor="#CFCFCF">Parentheses</td>
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<td align="center">Allowed</td>
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</tr>
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<tr>
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<td align="center" bgcolor="#CFCFCF">Nesting</td>
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<td align="center">Up to 16 levels</td>
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</tr>
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<tr>
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<td align="center" bgcolor="#CFCFCF">Related Commands</td>
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<td align="center" colspan="1">
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<p colspan="1" align="center"><a href="IF_THEN.htm" target="" title="" alt="" class="MCXref_0" xrefformat="{paratext}">IF…THEN</a>, <a href="SELECT_CASE.htm" target="" title="" alt="" class="MCXref_0" xrefformat="{paratext}">SELECT...CASE</a></p>
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</td>
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</tr>
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</table>
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<h2>Explanation</h2>
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<p class="PlainText"><span class="keyword_in_text">IF...THEN...ELSE</span> is a primary PBASIC decision maker that allows one block of
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code or [optionally] another to run based on the value (True or False) of a condition.
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The condition that <span class="keyword_in_text">IF...THEN...ELSE</span> tests is written as a mixture of
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comparison and logic operators. The available comparison operators are:</p>
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<center>
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<table cellpadding="4" cellspacing="0" border="1">
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<tr>
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<td width="130" align="center" bgcolor="#CFCFCF">Comparison Operator Symbol</td>
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<td width="170" align="center" bgcolor="#CFCFCF">Definition</td>
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</tr>
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<tr>
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<td align="center">=</td>
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<td align="center">Equal</td>
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</tr>
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<tr>
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<td align="center"><></td>
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<td align="center">Not Equal</td>
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</tr>
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<tr>
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<td align="center">></td>
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<td align="center">Greater Than</td>
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</tr>
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<tr>
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<td align="center"><</td>
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<td align="center">Less Than</td>
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</tr>
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<tr>
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<td align="center">>=</td>
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<td align="center">Greater Than or Equal To</td>
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</tr>
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<tr>
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<td align="center"><=</td>
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<td align="center">Less Than or Equal To</td>
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</tr>
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</table>
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</center>
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<p> </p>
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<p class="PlainText">Comparisons are always written in the form: <i>Value1 Comparison Value2</i>. The values
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to be compared can be any combination of variables (any size), constants, or
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expressions.</p><pre class="BScode" xml:space="preserve">
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value VAR Word
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Main:
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DO
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PULSIN 0, 1, value ' measure pulse input
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DEBUG DEC value, CR
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IF (value > 4000) THEN ' evaluate duration
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DEBUG "Value was greater than 4000"
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ELSEIF (value = 4000) THEN
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DEBUG "Value was equal to 4000"
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ELSE
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DEBUG "Value was less than 4000"
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ENDIF
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DEBUG CR, CR
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PAUSE 1000
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LOOP
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</pre>
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<p class="PlainText">Here, the BASIC Stamp will look for and measure a pulse on I/O pin 0, then
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compare the result, value, against 4000. Based on this comparison, a message
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regarding the pulse width value will be printed.</p>
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<p class="PlainText">In the following example, single-line syntax is used. Note that <span class="keyword_in_text">ENDIF</span>
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is not required when using single-line formatting of <span class="keyword_in_text">IF...THEN...ELSE</span>:
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</p><pre class="BScode" xml:space="preserve">
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DEBUG "Your grade is: "
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IF (score >= 90) THEN DEBUG "A", CR : ELSE DEBUG "B (or less)", CR
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</pre>
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<p class="PlainText">See <a href="IF_THEN.htm" target="" title="" alt="" class="MCXref_0" xrefformat="{paratext}">IF…THEN</a> for additional details on the use of
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comparison and conditional operators. </p>
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<p MadCap:conditions="BSEconditions.BSEWebHelp (Primary)-INCLUDE"><a href="../../HomeTopics/HomePage.htm">Go to Welcome page</a>
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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>
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<p style="text-align: right;">Copyright © <span class="ContactInfoCompanyName">Parallax Inc.</span></p>
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<p style="text-align: right;"><span class="SystemShortDate">8/8/2012</span>
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