title: How do you convert char numbers to decimal and back or convert ASCII 'A'-'Z'/'a'-'z' to letter offsets 0 for 'A'/'a' ...?
body: <p>If you have a char that is in the range '0' to '9' how do you convert it to int values of 0 to 9</p>
  
  <p>And then how do you convert it back?</p>
  
  <p>Also given letters 'A' to 'Z' or 'a' to 'z' how do you convert them to the range 0-25 and then back?</p>
  
  <p>It is okay to optimize for ASCII</p>