title: What's the diffrence between \xFF and 0xFF
body: <p>1st - What's the difference between</p>
  
  <pre><code>#define s 0xFF
  </code></pre>
  
  <p>and</p>
  
  <pre><code>#define s '\xFF'
  </code></pre>
  
  <p>2nd - Why the second line equals to -1? 
  3rd - Why after I try this (in the case of '\xFF')</p>
  
  <pre><code>unsigned char t = s;
  putchar(t);
  unsigned int p = s;
  printf("\n%d\n", p);
  </code></pre>
  
  <p>the output is</p>
  
  <pre><code>(blank)
  -1
  </code></pre>
  
  <p>?</p>
  
  <p>thanks:)</p>