[.net] String manipulation

hi, pls excused me for asking a newbie question, but how do i extract individual char out of a string? For example, i have a string(called field)which contains 13 letters, how do i loop through the string and extract each char inside of it? for (int i = 0; i< 13; i++) { switch (field(i)) <--- Obviously wrong, but what should i put in there? { case "w": .... break; case "e": .... break; . . . default: break; } } Thanks in advance for the helps.