title: Defining floating point constants, how many digits are useful?
body: <p>When I define constants in C that cannot be accurately represented in the decimal system, say for example <code>π</code>, how many digits will be taken into account by the compiler for actually creating the <code>float</code> or <code>double</code> in memory?</p>
  
  <p>For example:</p>
  
  <pre><code>/* Overkill? */
  const float PI_F = 3.1415926535897932384626433832795f;
  
  /* Too few digits? */
  const double PI_D = 3.14159;
  </code></pre>