Replacing several different characters in NSString - objective-c

Question

I am making an iPad app for personal use and I m struggling with some character replacement in some strings. For example I got an NSString which contains "\t\t\t C D". Now what I want to do is replace every C and every D there is in there with C# and D#. I have managed to do that but unfortunately it doesn't look efficient at all to me.
Here is my code so far:
- (IBAction)buttonPressed:(id)sender
{
if(sender)
{
NSError *error;
NSString *newTab = [[NSString alloc] init];
NSRegularExpression *regexC = [NSRegularExpression regularExpressionWithPattern:#"C" options:0 error:&error];
NSRegularExpression *regexD = [NSRegularExpression regularExpressionWithPattern:#"D" options:0 error:&error];
newTab = [regexC stringByReplacingMatchesInString:self.tab options:0 range:NSMakeRange(0, self.tab.length) withTemplate:#"C#"];
NSString *newTabAfterFirstRegex = [[NSString alloc] initWithString:newTab];
newTabAfterFirstRegex = [regexD stringByReplacingMatchesInString:newTab options:0 range:NSMakeRange(0, newTab.length) withTemplate:#"D#"];
NSLog(#"%#",newTabAfterFirstRegex);
}
}
Plus this is just a small tester code. What I would really like to do is to have an algorithm that checks for instances of all music tabs (C C# D D# E F F# G G# A A# B) in a given string and when the IBAction is triggered I would like each one of them to be replaced by the next one (and B becomes C).
Any ideas would be very much appreciated!
Thank you very much!

Answer 1

You can set a regular expression (e.g. '[A-G]#?') to match certain strings. With method -matchesInString:options:range: you can loop through all the matches (it will give back a range for each match) and use that range to do the replacements.

Answer 2

Regular expressions seem a bit like overkill for this, you could just do two string replacements, so that you don't get all the overhead from regexes, using
- (NSString *)stringByReplacingOccurrencesOfString:(NSString *)target
withString:(NSString *)replacement
and just replace it twice. Also, you don't need to do the NSString allocations, because it creates a reference in the return.

Answer 3

I created the following methods for encryption the other day. I've tested it for your purpose, and it seems to work.
-(NSString *)ReplaceMe:(NSString *)s {
// Putting the source into an array
NSMutableArray *myArray = [[NSMutableArray alloc] init];
int i;
for (i = 0; i < s.length; i++) {
[myArray addObject: [self Mid:s :i :1]];
}
// Creating a string with the revised array
NSMutableString *myString = [NSMutableString new];
for (i = 0; i < s.length; i++) {
[myString appendString:[self Conversion:[myArray objectAtIndex:i]]];
}
// Final
return myString;
}
The method above requires two additional functions.
-(NSString *)Mid:(NSString *)str:(NSInteger)s:(NSInteger)l {
if ((s <= str.length-1) && (s + l <= str.length) && (s >= 0) && (l >= 1)) {
return [str substringWithRange:NSMakeRange(s, l)];
}
else {
return #"";
}
}
The other is...
-(NSString *)Conversion:(NSString *)s {
if ([s isEqualToString:#"C"]) {
return #"C#";
}
else if ([s isEqualToString:#"D"]) {
return #"D#";
}
else {
return s;
}
}
You can put other conversion pairs in the function above. The following is an example as to how to use ReplaceMe.
- (IBAction)clickAction:(id)sender {
textField2.text = [self ReplaceMe:textField1.text];
}
So it's ReplaceMe is quite easy to use.