title: Byte to signed int in C
body: <p>I have a binary value stored in a char in C, I want transform this byte into signed int in C. 
  Currently I have something like this:</p>
  
  <pre><code>char a = 0xff;
  int b = a; 
  printf("value of b: %d\n", b);
  </code></pre>
  
  <p>The result in standard output will be "255", the desired output is "-1".</p>