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.