 <p>If you want to avoid using valid values of <code>float</code>, you could use a NAN:</p> <pre><code>#include &lt;limits&gt; .... float min = std::numeric_limits&lt;float&gt;::quiet_NaN(); </code></pre> <p>You can then use <code>std::isnan</code> to check:</p> <pre><code>#include &lt;cmath&gt; .... bool not_cool = std::isnan(min); </code></pre>