Shift Cipher Range out of Bounds
#define LETTER_POS 97
#define ALPHABET_LENGTH 26

- (NSString*)encode:(NSString*)original withShift:(int)shift {

    NSMutableString* encoded = [NSMutableString stringWithString:original];
    for (int i=0; i < [encoded length]; i++) {
        char oriChar = [encoded characterAtIndex:i];
        if (oriChar == ' ') {
            continue;
        }
        char encChar = ((oriChar - LETTER_POS) + shift) % ALPHABET_LENGTH + LETTER_POS;
        NSRange range = {i, i+1};
        [encoded replaceCharactersInRange:range withString:[NSString stringWithFormat:@"%c" , encChar]];

    }
    return encoded;

}