rogramming by contract</strong></span></em></span> with no
          runtime cost.</p></li>
<li class="listitem"><p>In addition, we define <code class="computeroutput">input_safe_t</code> to be used
          when reading variables from the program console. Clearly, these can
          only be checked at runtime so they use the throw_exception policy.
          When variables are read from the console they are checked for legal
          values. We need no ad hoc code to do this, as these types are
        