If Integer is instantiated, converts it to its corresponding one-character string.
Success: char_int("b",98). char_int(C,99). (gives C="c"). char_int("a",I). (gives I=97). Fail: char_int("a",98). Error: char_int(C,I). (Error 4). char_int("ab",I). (Error 5). char_int('a',I). (Error 5). char_int(C,'30'). (Error 5). char_int(C,128). (Error 6).