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<td >Qt 5.9</td><td ><a href="qtwidgets-index.html">Qt Widgets</a></td><td >Factorial States Example</td></tr></table><table class="buildversion"><tr>
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<h1 class="title">Factorial States Example</h1>
<span class="subtitle"></span>
<!-- $$$statemachine/factorial-description -->
<div class="descr"> <a name="details"></a>
<p>The statechart for calculating the factorial looks as follows:</p>
<p class="centerAlign"><img src="images/factorial-example.png" alt="" /></p><p>In other words, the state machine calculates the factorial of 6 and prints the result.</p>
<pre class="cpp">
<span class="keyword">class</span> Factorial : <span class="keyword">public</span> <span class="type"><a href="../qtcore/qobject.html">QObject</a></span>
{
Q_OBJECT
Q_PROPERTY(<span class="type">int</span> x READ x WRITE setX)
Q_PROPERTY(<span class="type">int</span> fac READ fac WRITE setFac)
<span class="keyword">public</span>:
Factorial(<span class="type"><a href="../qtcore/qobject.html">QObject</a></span> <span class="operator">*</span>parent <span class="operator">=</span> <span class="number">0</span>)
: <span class="type"><a href="../qtcore/qobject.html">QObject</a></span>(parent)<span class="operator">,</span> m_x(<span class="operator">-</span><span class="number">1</span>)<span class="operator">,</span> m_fac(<span class="number">1</span>)
{
}
<span class="type">int</span> x() <span class="keyword">const</span>
{
<span class="keyword">return</span> m_x;
}
<span class="type">void</span> setX(<span class="type">int</span> x)
{
<span class="keyword">if</span> (x <span class="operator">=</span><span class="operator">=</span> m_x)
<span class="keyword">return</span>;
m_x <span class="operator">=</span> x;
<span class="keyword">emit</span> xChanged(x);
}
<span class="type">int</span> fac() <span class="keyword">const</span>
{
<span class="keyword">return</span> m_fac;
}
<span class="type">void</span> setFac(<span class="type">int</span> fac)
{
m_fac <span class="operator">=</span> fac;
}
Q_SIGNALS:
<span class="type">void</span> xChanged(<span class="type">int</span> value);
<span class="keyword">private</span>:
<span class="type">int</span> m_x;
<span class="type">int</span> m_fac;
};
</pre>
<p>The Factorial class is used to hold the data of the computation, <code>x</code> and <code>fac</code>. It also provides a signal that's emitted whenever the value of <code>x</code> changes.</p>
<pre class="cpp">
<span class="keyword">class</span> FactorialLoopTransition : <span class="keyword">public</span> <span class="type"><a href="../qtcore/qsignaltransition.html">QSignalTransition</a></span>
{
<span class="keyword">public</span>:
FactorialLoopTransition(Factorial <span class="operator">*</span>fact)
: <span class="type"><a href="../qtcore/qsignaltransition.html">QSignalTransition</a></span>(fact<span class="operator">,</span> SIGNAL(xChanged(<span class="type">int</span>)))<span class="operator">,</span> m_fact(fact)
{}
bool eventTest(<span class="type"><a href="../qtcore/qevent.html">QEvent</a></span> <span class="operator">*</span>e) override
{
<span class="keyword">if</span> (<span class="operator">!</span><span class="type"><a href="../qtcore/qsignaltransition.html">QSignalTransition</a></span><span class="operator">::</span>eventTest(e))
<span class="keyword">return</span> <span class="keyword">false</span>;
<span class="type"><a href="../qtcore/qstatemachine.html">QStateMachine</a></span><span class="operator">::</span>SignalEvent <span class="operator">*</span>se <span class="operator">=</span> <span class="keyword">static_cast</span><span class="operator"><</span><span class="type"><a href="../qtcore/qstatemachine.html">QStateMachine</a></span><span class="operator">::</span>SignalEvent<span class="operator">*</span><span class="operator">></span>(e);
<span class="keyword">return</span> se<span class="operator">-</span><span class="operator">></span>arguments()<span class="operator">.</span>at(<span class="number">0</span>)<span class="operator">.</span>toInt() <span class="operator">></span> <span class="number">1</span>;
}
<span class="type">void</span> onTransition(<span class="type"><a href="../qtcore/qevent.html">QEvent</a></span> <span class="operator">*</span>e) override
{
<span class="type"><a href="../qtcore/qstatemachine.html">QStateMachine</a></span><span class="operator">::</span>SignalEvent <span class="operator">*</span>se <span class="operator">=</span> <span class="keyword">static_cast</span><span class="operator"><</span><span class="type"><a href="../qtcore/qstatemachine.html">QStateMachine</a></span><span class="operator">::</span>SignalEvent<span class="operator">*</span><span class="operator">></span>(e);
<span class="type">int</span> x <span class="operator">=</span> se<span class="operator">-</span><span class="operator">></span>arguments()<span class="operator">.</span>at(<span class="number">0</span>)<span class="operator">.</span>toInt();
<span class="type">int</span> fac <span class="operator">=</span> m_fact<span class="operator">-</span><span class="operator">></span>property(<span class="string">"fac"</span>)<span class="operator">.</span>toInt();
m_fact<span class="operator">-</span><span class="operator">></span>setProperty(<span class="string">"fac"</span><span class="operator">,</span> x <span class="operator">*</span> fac);
m_fact<span class="operator">-</span><span class="operator">></span>setProperty(<span class="string">"x"</span><span class="operator">,</span> x <span class="operator">-</span> <span class="number">1</span>);
}
<span class="keyword">private</span>:
Factorial <span class="operator">*</span>m_fact;
};
</pre>
<p>The FactorialLoopTransition class implements the guard (<code>x</code> > 1) and calculations (<code>fac</code> = <code>x</code> * <code>fac</code>; <code>x</code> = <code>x</code> - 1) of the factorial loop.</p>
<pre class="cpp">
<span class="keyword">class</span> FactorialDoneTransition : <span class="keyword">public</span> <span class="type"><a href="../qtcore/qsignaltransition.html">QSignalTransition</a></span>
{
<span class="keyword">public</span>:
FactorialDoneTransition(Factorial <span class="operator">*</span>fact)
: <span class="type"><a href="../qtcore/qsignaltransition.html">QSignalTransition</a></span>(fact<span class="operator">,</span> SIGNAL(xChanged(<span class="type">int</span>)))<span class="operator">,</span> m_fact(fact)
{}
bool eventTest(<span class="type"><a href="../qtcore/qevent.html">QEvent</a></span> <span class="operator">*</span>e) override
{
<span class="keyword">if</span> (<span class="operator">!</span><span class="type"><a href="../qtcore/qsignaltransition.html">QSignalTransition</a></span><span class="operator">::</span>eventTest(e))
<span class="keyword">return</span> <span class="keyword">false</span>;
<span class="type"><a href="../qtcore/qstatemachine.html">QStateMachine</a></span><span class="operator">::</span>SignalEvent <span class="operator">*</span>se <span class="operator">=</span> <span class="keyword">static_cast</span><span class="operator"><</span><span class="type"><a href="../qtcore/qstatemachine.html">QStateMachine</a></span><span class="operator">::</span>SignalEvent<span class="operator">*</span><span class="operator">></span>(e);
<span class="keyword">return</span> se<span class="operator">-</span><span class="operator">></span>arguments()<span class="operator">.</span>at(<span class="number">0</span>)<span class="operator">.</span>toInt() <span class="operator"><</span><span class="operator">=</span> <span class="number">1</span>;
}
<span class="type">void</span> onTransition(<span class="type"><a href="../qtcore/qevent.html">QEvent</a></span> <span class="operator">*</span>) override
{
fprintf(stdout<span class="operator">,</span> <span class="string">"%d\n"</span><span class="operator">,</span> m_fact<span class="operator">-</span><span class="operator">></span>property(<span class="string">"fac"</span>)<span class="operator">.</span>toInt());
}
<span class="keyword">private</span>:
Factorial <span class="operator">*</span>m_fact;
};
</pre>
<p>The FactorialDoneTransition class implements the guard (<code>x</code> <= 1) that terminates the factorial computation. It also prints the final result to standard output.</p>
<pre class="cpp">
<span class="type">int</span> main(<span class="type">int</span> argc<span class="operator">,</span> <span class="type">char</span> <span class="operator">*</span><span class="operator">*</span>argv)
{
<span class="type"><a href="../qtcore/qcoreapplication.html">QCoreApplication</a></span> app(argc<span class="operator">,</span> argv);
Factorial factorial;
<span class="type"><a href="../qtcore/qstatemachine.html">QStateMachine</a></span> machine;
</pre>
<p>The application's main() function first creates the application object, a Factorial object and a state machine.</p>
<pre class="cpp">
<span class="type"><a href="../qtcore/qstate.html">QState</a></span> <span class="operator">*</span>compute <span class="operator">=</span> <span class="keyword">new</span> <span class="type"><a href="../qtcore/qstate.html">QState</a></span>(<span class="operator">&</span>machine);
compute<span class="operator">-</span><span class="operator">></span>assignProperty(<span class="operator">&</span>factorial<span class="operator">,</span> <span class="string">"fac"</span><span class="operator">,</span> <span class="number">1</span>);
compute<span class="operator">-</span><span class="operator">></span>assignProperty(<span class="operator">&</span>factorial<span class="operator">,</span> <span class="string">"x"</span><span class="operator">,</span> <span class="number">6</span>);
compute<span class="operator">-</span><span class="operator">></span>addTransition(<span class="keyword">new</span> FactorialLoopTransition(<span class="operator">&</span>factorial));
</pre>
<p>The <code>compute</code> state is created, and the initial values of <code>x</code> and <code>fac</code> are defined. A FactorialLoopTransition object is created and added to the state.</p>
<pre class="cpp">
<span class="type"><a href="../qtcore/qfinalstate.html">QFinalState</a></span> <span class="operator">*</span>done <span class="operator">=</span> <span class="keyword">new</span> <span class="type"><a href="../qtcore/qfinalstate.html">QFinalState</a></span>(<span class="operator">&</span>machine);
FactorialDoneTransition <span class="operator">*</span>doneTransition <span class="operator">=</span> <span class="keyword">new</span> FactorialDoneTransition(<span class="operator">&</span>factorial);
doneTransition<span class="operator">-</span><span class="operator">></span>setTargetState(done);
compute<span class="operator">-</span><span class="operator">></span>addTransition(doneTransition);
</pre>
<p>A final state, <code>done</code>, is created, and a FactorialDoneTransition object is created with <code>done</code> as its target state. The transition is then added to the <code>compute</code> state.</p>
<pre class="cpp">
machine<span class="operator">.</span>setInitialState(compute);
<span class="type"><a href="../qtcore/qobject.html">QObject</a></span><span class="operator">::</span>connect(<span class="operator">&</span>machine<span class="operator">,</span> SIGNAL(finished())<span class="operator">,</span> <span class="operator">&</span>app<span class="operator">,</span> SLOT(quit()));
machine<span class="operator">.</span>start();
<span class="keyword">return</span> app<span class="operator">.</span>exec();
}
</pre>
<p>The machine's initial state is set to be the <code>compute</code> state. We connect the <a href="../qtcore/qstate.html#finished">QStateMachine::finished</a>() signal to the <a href="../qtcore/qcoreapplication.html#quit">QCoreApplication::quit</a>() slot, so the application will quit when the state machine's work is done. Finally, the state machine is started, and the application's event loop is entered.</p>
<p>Files:</p>
<ul>
<li><a href="qtwidgets-statemachine-factorial-main-cpp.html">statemachine/factorial/main.cpp</a></li>
<li><a href="qtwidgets-statemachine-factorial-factorial-pro.html">statemachine/factorial/factorial.pro</a></li>
</ul>
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<!-- @@@statemachine/factorial -->
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