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Chapters:
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<a href="Introduction.html">1: Introduction</a><br>
<a href="SimpleExample.html">2: Simple example</a><br>
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<h3>9.3.16: `<font color="#82140F"><code>if</code></font>'</h3>
<!-- latex: \index{if} -->
(<b>See also</b> see <a href="IfStatements.html#IfStatements">If Statements</a>.)
<p>
<TABLE SUMMARY="Example" BORDER="0" BGCOLOR="#efefef" WIDTH="100%">
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<PRE>
<font color="#82140F">
`if {[!] .flag.}|\flag|{{"string1" == "string2"}}'
</font></PRE>
</TD>
</TR>
</TABLE>
<p>
Control program flow. The `<font color="#82140F"><code>if</code></font>' block is ended with a line
containing `<font color="#82140F"><code>end if</code></font>'. Optional `<font color="#82140F"><code>else</code></font>' and `<font color="#82140F"><code>else if</code></font>'
blocks are allowed. Note that rpn expressions are allowed, and a
special form of string comparison is allowed, as in the examples below.
<p>
<TABLE SUMMARY="Example" BORDER="0" BGCOLOR="#efefef" WIDTH="100%">
<TR>
<TD>
<PRE>
<font color="#82140F">
if .flag.
# List of Gri commands to be done if .flag. is 1.
# This list may extend across any number of lines.
end if
</font></PRE>
</TD>
</TR>
</TABLE>
<p>
If the variable `<font color="#82140F"><code>.flag.</code></font>' is not equal to 0, do the code between the
`<font color="#82140F"><code>if</code></font>' line and the `<font color="#82140F"><code>end if</code></font>' line.
<p>
<TABLE SUMMARY="Example" BORDER="0" BGCOLOR="#efefef" WIDTH="100%">
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<PRE>
<font color="#82140F">
if .flag.
# Commands done if .flag. is 1
else
# Commands done if .flag. is 0
end if
</font></PRE>
</TD>
</TR>
</TABLE>
<p>
If the variable `<font color="#82140F"><code>.flag.</code></font>' is not equal to 0, do the code between the
`<font color="#82140F"><code>if</code></font>' line and the `<font color="#82140F"><code>else</code></font>' line. If `<font color="#82140F"><code>.flag.</code></font>' is equal to
0, do the code between the `<font color="#82140F"><code>else</code></font>' line and the `<font color="#82140F"><code>end if</code></font>' line.
<p>
<TABLE SUMMARY="Example" BORDER="0" BGCOLOR="#efefef" WIDTH="100%">
<TR>
<TD>
<PRE>
<font color="#82140F">
if ! .flag.
# Commands done if .flag. is 0
end if
</font></PRE>
</TD>
</TR>
</TABLE>
<p>
If the variable `<font color="#82140F"><code>.flag.</code></font>' is equal to 0, do the code between the
`<font color="#82140F"><code>if</code></font>' line and the `<font color="#82140F"><code>end if</code></font>' line.
<p>
<TABLE SUMMARY="Example" BORDER="0" BGCOLOR="#efefef" WIDTH="100%">
<TR>
<TD>
<PRE>
<font color="#82140F">
if {rpn .flag. 10 <}
# Commands done if 10 is less than .flag.
end if
</font></PRE>
</TD>
</TR>
</TABLE>
<p>
If the variable `<font color="#82140F"><code>.flag.</code></font>' is greater than 10,
do the code between the
`<font color="#82140F"><code>if</code></font>' line and the `<font color="#82140F"><code>end if</code></font>' line.
<p>
<TABLE SUMMARY="Example" BORDER="0" BGCOLOR="#efefef" WIDTH="100%">
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<TD>
<PRE>
<font color="#82140F">
if \smooth
# Commands done if \smooth is 1
else
# Commands done if \smooth is 0
end if
</font></PRE>
</TD>
</TR>
</TABLE>
<p>
If the number stored in the synonym `<font color="#82140F"><code>\smooth</code></font>' is not equal to 0, do
the code between the `<font color="#82140F"><code>if</code></font>' line and the `<font color="#82140F"><code>else</code></font>' line. If the
synonym stores a representation of a number not equal to zero, do the
`<font color="#82140F"><code>else</code></font>' part. If the synonym contains text that does not decode to
a number, generate error message.
<p>
<TABLE SUMMARY="Example" BORDER="0" BGCOLOR="#efefef" WIDTH="100%">
<TR>
<TD>
<PRE>
<font color="#82140F">
if {"\item" == "Temperature"}
# Commands done if the synonym \item is equal to the
# indicated text string.
end if
</font></PRE>
</TD>
</TR>
</TABLE>
<p>
If the synonym `<font color="#82140F"><code>\item</code></font>' has the value `<font color="#82140F"><code>Temperature</code></font>' stored in
it, do the indicated code.
<p>
<TABLE SUMMARY="Example" BORDER="0" BGCOLOR="#efefef" WIDTH="100%">
<TR>
<TD>
<PRE>
<font color="#82140F">
if {rpn "\item" "Temperature" ==}
# Commands done if the synonym \item
# equals indicated text string.
end if
</font></PRE>
</TD>
</TR>
</TABLE>
<p>
As above, but using the `<font color="#82140F"><code>rpn</code></font>' calculator
(see <a href="ReversePolishMath.html#rpnMathematics">rpn Mathematics</a>).
<p>
<TABLE SUMMARY="Example" BORDER="0" BGCOLOR="#efefef" WIDTH="100%">
<TR>
<TD>
<PRE>
<font color="#82140F">
if {rpn "\item" "Temperature" !=}
# ...
end if
</font></PRE>
</TD>
</TR>
</TABLE>
<p>
As above, but do the indicated code if `<font color="#82140F"><code>\item</code></font>' is <b>not</b> equal
to `<font color="#82140F"><code>Temperature</code></font>'.
<p>
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