title: Char to int conversion in C
body: <p>If I want to convert a single numeric <code>char</code> to it's numeric value, for example, if:</p>
  
  <pre><code>char c = '5';
  </code></pre>
  
  <p>and I want <code>c</code> to hold <code>5</code> instead of <code>'5'</code>, is it 100% portable doing it like this?</p>
  
  <pre><code>c = c - '0';
  </code></pre>
  
  <p>I heard that all character sets store the numbers in consecutive order so I assume so, but I'd like to know if there is an organized library function to do this conversion, and how it is done conventionally. I'm a real beginner :)</p>