title: exit(); is not working
body: <p>In my programming book, it shows me exit used without any parameters(<code>exit();</code>).
  Unfortunately it does not work.</p>
  
  <p>Some people have said use <code>exit(0);</code> while some say <code>exit(1); exit(2);</code> and <code>exit(3)</code>;
  What is the difference between them and is there even an <code>exit(4);</code> ?</p>
  
  <p>The funny thing is that my compiler does not need <code>stdlib.h</code> to execute <code>exit(0);</code> and the rest.</p>