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<refentry id="if">
<indexterm id="IndexIf"><primary>if</primary></indexterm>
<refentryinfo><title>Instrument Control:Program Flow Control</title></refentryinfo>
<refmeta>
<refentrytitle>if</refentrytitle>
</refmeta>
<refnamediv>
<refname>if</refname>
<refpurpose>
Branches conditionally at initialization or during performance time.
</refpurpose>
</refnamediv>
<refsect1>
<title>Description</title>
<para>
<emphasis>if...igoto</emphasis> -- conditional branch at initialization time, depending on the truth value of the logical expression <emphasis>ia</emphasis> <emphasis>R</emphasis> <emphasis>ib</emphasis>. The branch is taken only if the result is true.
</para>
<para>
<emphasis>if...kgoto</emphasis> -- conditional branch during performance time, depending on the truth value of the logical expression <emphasis>ka</emphasis> <emphasis>R</emphasis> <emphasis>kb</emphasis>. The branch is taken only if the result is true.
</para>
<para>
<emphasis>if...goto</emphasis> -- combination of the above. Condition tested on every pass.
</para>
<para>
<emphasis>if...then</emphasis> -- allows the ability to specify conditional <emphasis>if</emphasis>/<emphasis>else</emphasis>/<emphasis>endif</emphasis> blocks. All <emphasis>if...then</emphasis> blocks must end with an <emphasis>endif</emphasis> statement. <emphasis>elseif</emphasis> and <emphasis>else</emphasis> statements are optional. Any number of <emphasis>elseif</emphasis> statements are allowed. Only one <emphasis>else</emphasis> statement may occur and it must be the last conditional statement before the <emphasis>endif</emphasis> statement. Nested <emphasis>if...then</emphasis> blocks are allowed.
</para>
<note>
<title>Note</title>
<para>
Note that if the condition uses a k-rate variable (for instance, <quote>if kval > 0</quote>), the <emphasis>if...goto</emphasis> or <emphasis>if...then</emphasis> statement will be ignored during the i-time pass. This allows for opcode initialization, even if the k-rate variable has already been assigned an appropriate value by an earlier init statement.
</para>
</note>
</refsect1>
<refsect1>
<title>Syntax</title>
<synopsis><command>if</command> ia R ib <command>igoto</command> label</synopsis>
<synopsis><command>if</command> ka R kb <command>kgoto</command> label</synopsis>
<synopsis><command>if</command> ia R ib <command>goto</command> label</synopsis>
<synopsis><command>if</command> xa R xb <command>then</command></synopsis>
<para>
where <emphasis>label</emphasis> is in the same instrument block and is not an expression, and where <emphasis>R</emphasis> is one of the Relational operators (<emphasis><</emphasis>, <emphasis>=</emphasis>, <emphasis><=</emphasis>, <emphasis>==</emphasis>, <emphasis>!=</emphasis>) (and <emphasis>=</emphasis> for convenience, see also under <link linkend="ControlConditional"><citetitle>Conditional Values</citetitle></link>).
</para>
</refsect1>
<refsect1>
<title>Examples</title>
<para>
Here is an example of the if...igoto combination. It uses the file <ulink url="examples/igoto.csd"><citetitle>igoto.csd</citetitle></ulink>.
<example>
<title>Example of the if...igoto combination.</title>
<para>See the sections <link linkend="UsingRealTime"><citetitle>Real-time Audio</citetitle></link> and <link linkend="CommandFlags"><citetitle>Command Line Flags</citetitle></link> for more information on using command line flags.</para>
<xi:include href="examples-xml/igoto.csd.xml" xmlns:xi="http://www.w3.org/2001/XInclude"/>
</example>
Its output should include lines like this:
<screen>
instr 1: iparam = 0.000
instr 1: ifreq = 440.000
instr 1: iparam = 1.000
instr 1: ifreq = 880.000
</screen>
</para>
<para>
Here is an example of the if...kgoto combination. It uses the file <ulink url="examples/kgoto.csd"><citetitle>kgoto.csd</citetitle></ulink>.
<example>
<title>Example of the if...kgoto combination.</title>
<xi:include href="examples-xml/kgoto.csd.xml" xmlns:xi="http://www.w3.org/2001/XInclude"/>
</example>
Its output should include lines like this:
<screen>
kval = 0.000000, kfreq = 440.000000
kval = 0.999732, kfreq = 440.000000
kval = 1.999639, kfreq = 880.000000
</screen>
</para>
</refsect1>
<refsect1>
<title>Examples</title>
<para>
Here is an example of the if...then combo. It uses the file <ulink url="examples/ifthen.csd"><citetitle>if.csd</citetitle></ulink>.
<example>
<title>Example of the if...then combo.</title>
<programlisting>
<!--<xi:include href="examples/ifthen.csd" parse="text" xmlns:xi="http://www.w3.org/2001/XInclude"/>-->
</programlisting>
</example>
</para>
</refsect1>
<refsect1>
<title>See Also</title>
<para>
<link linkend="elseif"><citetitle>elseif</citetitle></link>,
<link linkend="else"><citetitle>else</citetitle></link>,
<link linkend="endif"><citetitle>endif</citetitle></link>,
<link linkend="goto"><citetitle>goto</citetitle></link>,
<link linkend="igoto"><citetitle>igoto</citetitle></link>,
<link linkend="kgoto"><citetitle>kgoto</citetitle></link>,
<link linkend="tigoto"><citetitle>tigoto</citetitle></link>,
<link linkend="timout"><citetitle>timout</citetitle></link>
</para>
</refsect1>
<refsect1>
<title>Credits</title>
<para>Examples written by &namekevin;.</para>
<para>Added a note by Jim Aikin.</para>
<para>February 2004. Added a note by &namematt;.</para>
</refsect1>
</refentry>
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