Detecting if a character is either a letter or a number

Question

In objective-c, how would I check if a single character was either a letter or a number? I would like to eliminate all other characters.

Answer 1

To eliminate non letters:

NSString *letters = @"abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
NSCharacterSet *notLetters = [[NSCharacterSet characterSetWithCharactersInString:letters] invertedSet];
NSString *newString = [[string componentsSeparatedByCharactersInSet:notLetters] componentsJoinedByString:@""];

To check one character at a time:

for (int i = 0; i < [string length]; i++) {
    unichar c = [string characterAtIndex:i];
    if ([notLetters characterIsMember:c]) { 
       ... 
    }
}