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<H1><A NAME="SECTION04090000000000000000"></A>
<A NAME="commands_if"></A><A NAME="if"></A><A NAME="2432"></A>
<BR>
If
</H1>
The <B>if</B> command allows commands to be executed conditionally.
<P>
Syntax:
<BR>
<PRE>
if (<condition>) <command-line> [; else if (<condition>) ...; else ...]
</PRE>
<BR>
<P>
4#4condition5#5 will be evaluated. If it is true (non-zero), then the command(s)
of the 4#4command-line5#5 will be executed. If 4#4condition5#5 is false (zero), then
the entire 4#4command-line5#5 is ignored until the next occurrence of <B>else</B>.
Note that use of <B>;</B> to allow multiple commands on the same line will
<EM>not</EM> end the conditionalized commands.
<P>
Examples:
<BR>
<PRE>
pi=3
if (pi!=acos(-1)) print "?Fixing pi!"; pi=acos(-1); print pi
</PRE>
<BR>
will display:
<BR>
<PRE>
?Fixing pi!
3.14159265358979
</PRE>
<BR>
but
<BR>
<PRE>
if (1==2) print "Never see this"; print "Or this either"
</PRE>
<BR>
will not display anything.
<P>
else:
<BR>
<PRE>
v=0
v=v+1; if (v%2) print "2" ; else if (v%3) print "3"; else print "fred"
</PRE>
<BR>
(repeat the last line repeatedly!)
<P>
See <B>reread (p. <A HREF="node172.html#reread"><IMG ALIGN="BOTTOM" BORDER="1" ALT="[*]" SRC="crossref.png"></A>)<A NAME="2448"></A></B> for an example of how <B>if (p. <A HREF="node108.html#if"><IMG ALIGN="BOTTOM" BORDER="1" ALT="[*]" SRC="crossref.png"></A>)<A NAME="2450"></A></B> and <B>reread (p. <A HREF="node172.html#reread"><IMG ALIGN="BOTTOM" BORDER="1" ALT="[*]" SRC="crossref.png"></A>)<A NAME="2452"></A></B> can be used together to
perform a loop.
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<ADDRESS>
2010-08-17
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