title: language c, compile time error multiple unsequenced modifications [-Werror, -Wunsequenced]
body: <p>Here is the defintion of my function:</p>
  
  <pre><code>char *strsub(char const *s, unsigned int start, size_t len){
     blabla
     blabla
     while (len &gt; 0)
     {
        len--;
        cpy[start++] = s[start++];
     }
  }
  </code></pre>
  
  <p>When I try to compile I get this error: </p>
  
  <blockquote>
    <p>error : multiple unsecquenced modifications to start -Werror , -Wunsequenced</p>
  </blockquote>
  
  <p>I don't understand that error at all.</p>