ROT13 encode/decode string but don't change characters within brackets [] - ios

Question

I have a simple ROT13 method that encodes or decodes a string.
+ (NSString *)ROT13encodeString:(NSString *)aString {
if (!aString) {
return nil;
}
// Find text between brackets
NSCharacterSet *delimiters = [NSCharacterSet characterSetWithCharactersInString:#"[]"];
NSArray *splitString = [aString componentsSeparatedByCharactersInSet:delimiters];
// ???
NSString *newString;
unsigned length;
unichar *buf;
unsigned i;
length = [aString length];
buf = malloc( (length + 1) * sizeof(unichar) );
[aString getCharacters:buf];
buf[length] = (unichar)0; // not really needed....
for (i = 0; i < length; i++) {
if (buf[i] >= (unichar)'a' && buf[i] <= (unichar) 'z') {
buf[i] += 13;
if (buf[i] > 'z') buf[i] -= 26;
} else if (buf[i] >= (unichar)'A' && buf[i] <= (unichar) 'Z') {
buf[i] += 13;
if (buf[i] > 'Z') buf[i] -= 26;
}
}
newString = [NSString stringWithCharacters:buf length:length];
free(buf);
return newString;
}
However, within the text to encode, there are "safe" words that are placed within brackets []. The words, including the brackets should never be encoded, they always need to be in their non-encoded state.
I figured I could pull out all occururances of the bracketed text, but not sure how it would help:
NSCharacterSet *delimiters = [NSCharacterSet characterSetWithCharactersInString:#"[]"];
NSArray *splitString = [aString componentsSeparatedByCharactersInSet:delimiters];
How could I modify my current method to include this?

Answer 1

I don't code in objective-c, but I think this should be close:
+ (NSString *)ROT13encodeString:(NSString *)aString {
if (!aString) {
return nil;
}
// Find text between brackets
NSCharacterSet *delimiters = [NSCharacterSet characterSetWithCharactersInString:#"[]"];
NSArray *splitString = [aString componentsSeparatedByCharactersInSet:delimiters];
// ???
NSString *newString;
unsigned length;
unichar *buf;
unsigned i;
unsigned level;
length = [aString length];
buf = malloc( (length + 1) * sizeof(unichar) );
[aString getCharacters:buf];
buf[length] = (unichar)0; // not really needed....
level = 0;
for (i = 0; i < length; i++) {
if (buf[i] == (unichar)'[') {
level++;
} else if (buf[i] == (unichar)']') {
level--;
} else if (level==0 && buf[i] >= (unichar)'a' && buf[i] <= (unichar) 'z') {
buf[i] += 13;
if (buf[i] > 'z') buf[i] -= 26;
} else if (level==0 && buf[i] >= (unichar)'A' && buf[i] <= (unichar) 'Z') {
buf[i] += 13;
if (buf[i] > 'Z') buf[i] -= 26;
}
}
newString = [NSString stringWithCharacters:buf length:length];
free(buf);
return newString;
}