You can add or subtract from a char to move through the alphabet. 'A' + 1 gives you 'B'. 'z' - 1 gives you 'y'. To convert a digit character to its numeric value, subtract '0': int num = '5' - '0'; gives you 5.
This works because '5' is 53 and '0' is 48, so 53 - 48 = 5. Example: char next = 'c' + 1; stores 'd'. You can loop through letters: for (char c = 'a'; c <= 'z'; c++) iterates from a to z.