title: Why the ASCII value of a digit character is equal to the value plus '0'?
body: <p>Why when we want to convert an ASCII value of a digit into an integer, we need to do:</p>
  
  <p><code>value - '0'</code> ?</p>
  
  <p>And the other way around, to convert Integer to ASCII, we need to do:</p>
  
  <pre><code>value + '0'
  </code></pre>
  
  <p>Why is that?</p>