26 letters
abcdefghijklmnopqrstuvwxyz
a-z: 97 - 122
A-Z: 65 - 90
Lowercase to uppercase: char-32
‘a’ - 32 -> A
Uppercase to lowercase: char + 32
‘A’ + 32 -> a
Get the ACSII corresponding number of the letter: forced to int (int) char
(int) ‘a’ -> 97
Number to letter: forced to char (char) int
(char) 97 -> a