title: Char shifting in C
body: <p>I am trying to find the function in the library that shifts chars back and forward as I want 
  for instance:</p>
  
  <p>if this function consumes 'a' and a number to shift forward 3 , it will be shifted 3 times and the output will be 'd'.</p>
  
  <p>if it this function consumes '5' and a number to shift forward 3 , it will be shifted 3 times and the output will be '8'.</p>
  
  <p>how can I achieve this?</p>