input: Write a function to rotate each character in a string by a given number of positions.
  assert rotateString("Hello", 3) == 'Khoor'
  assert rotateString("abcd", 1) == 'bcde'
  assert rotateString("xyz", 2) == 'z{'
  assert rotateString("Rotate", 5) == 'Wtyfyj'
  assert rotateString("Python", 0) == 'Python'
output: def rotateString(s, n):
      return ''.join(chr(ord(char) + n) for char in s)