evaluation.shtml
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<TITLE>Miscellaneous - In-Program Evaluation</TITLE>
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In-Program Evaluation
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This article was contributed by <!-- Author Email --><a href="mailto:Joachim.Raidl@iname.com">Joachim Raidl</A>.
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<p>In my projects I often need to evaluate expressions. So I
created a class that provides evaluation of expressions with the
posibility to declare variables and easy functions. For this
article I include the XEvaluate-class in a 'calculator'-dialog,
but normaly, I use the class in my application like this: XString
erg = Evaluate("1+2*sqr(3)").</p>
<p>!!! The XString-class that XEvaluate uses, was also
contributed at codeguru.</p>
<p>You can use external variables in a XDoubleMap. This typedef
is allready defined in XEvaluate.h (typedef CMap<CString,
LPCTSTR, double, double> XDoubleMap;):</p>
<pre><font color="#990000"> XDoubleMap var;
var["alpha"] = 10;
var["beta"] = 20;
var["test"] = 1.234;
double erg = dtoa(Evaluate("alpha+beta", var));
</font></pre>
<p>It's possible to use userdefined functions with one argument
(this argument has to be 'x')</p>
<pre><font color="#990000"> Evaluate("f:=sin(x)+cos(x)");
double erg = dtoa(Evaluate("f(pi/2)"));
</font></pre>
<p>You can also call Evaluate with more than one expression, if
you divide the expressions by a semikolon:</p>
<pre><font color="#990000"> double erg = dtoa(Evaluate("a=10;b=20;c=a+b");
</font></pre>
<p>The following functions and operations are included in
XEvaluate:</p>
<table border="1" cellspacing="1" width="100%">
<tr>
<td align="center">sin</td>
<td align="center">cos</td>
<td align="center">tan</td>
<td align="center"> </td>
<td align="center"> </td>
<td align="center"> </td>
<td>trigonometric functions</td>
</tr>
<tr>
<td align="center">asin</td>
<td align="center">acos</td>
<td align="center">atan</td>
<td align="center"> </td>
<td align="center"> </td>
<td align="center"> </td>
<td>inverse trigonometric functions</td>
</tr>
<tr>
<td align="center">rad</td>
<td align="center">deg</td>
<td align="center">gon</td>
<td align="center"> </td>
<td align="center"> </td>
<td align="center"> </td>
<td>trigonometric calculation type</td>
</tr>
<tr>
<td align="center">pow</td>
<td align="center">sqr</td>
<td align="center">sqrt</td>
<td align="center">exp</td>
<td align="center">log</td>
<td align="center">log10</td>
<td>power, square, squareroot, exp, natural log, tenth
log</td>
</tr>
<tr>
<td align="center">abs</td>
<td align="center">int</td>
<td align="center">fract</td>
<td align="center">fak</td>
<td align="center">cube</td>
<td align="center"> </td>
<td>absolute, integer part, factional part, n!, cube</td>
</tr>
<tr>
<td align="center">dec</td>
<td align="center">hex</td>
<td align="center">bin</td>
<td align="center">char</td>
<td align="center"> </td>
<td align="center"> </td>
<td>outputtype</td>
</tr>
<tr>
<td align="center">fix</td>
<td align="center"> </td>
<td align="center"> </td>
<td align="center"> </td>
<td align="center"> </td>
<td align="center"> </td>
<td>set the decimal digits</td>
</tr>
<tr>
<td align="center">+</td>
<td align="center">-</td>
<td align="center">*</td>
<td align="center">/</td>
<td align="center"> </td>
<td align="center"> </td>
<td>add, sub, mul, div</td>
</tr>
<tr>
<td align="center">%</td>
<td align="center">&</td>
<td align="center">|</td>
<td align="center">^</td>
<td align="center">!</td>
<td align="center">~</td>
<td>modulo, binary and, or, xor, not, binary not</td>
</tr>
<tr>
<td align="center"><</td>
<td align="center">></td>
<td align="center"><=</td>
<td align="center">>=</td>
<td align="center">==</td>
<td align="center">!=</td>
<td>less, greater, less or equal, greater or equal,
equal, not equal</td>
</tr>
<tr>
<td align="center">=</td>
<td align="center">+=</td>
<td align="center">-=</td>
<td align="center">*=</td>
<td align="center">/=</td>
<td align="center"> </td>
<td>variable setting</td>
</tr>
<tr>
<td align="center">@</td>
<td align="center"> </td>
<td align="center"> </td>
<td align="center"> </td>
<td align="center"> </td>
<td align="center"> </td>
<td>old value (result of the last calculation)</td>
</tr>
<tr>
<td align="center">?</td>
<td align="center"> </td>
<td align="center"> </td>
<td align="center"> </td>
<td align="center"> </td>
<td align="center"> </td>
<td>help (lists all functions)</td>
</tr>
<tr>
<td align="center">#</td>
<td align="center"> </td>
<td align="center"> </td>
<td align="center"> </td>
<td align="center"> </td>
<td align="center"> </td>
<td>reset (delete all functions and variables)</td>
</tr>
<tr>
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