Question

I’m having a rather annoying problem here. See, I’m trying to break up a string that I get into individual characters and symbols. The string is always in the form of an equation, like “3x+4” or “x/7+5”. I need to separate the string into an array of individual strings. For example, if I had the first equation, I would want to have an NSMutableArray that has “3”, “x”, “+”, and “4”. Here is the section of code that I use:

NSMutableArray* list = [[NSMutableArray alloc] initWithCapacity:10];
for (int i = 0; i < [self.equationToGuess length]; i++) {
    NSRange range = {i, i};
    NSString* string= [[NSString alloc] initWithString:[self.equationToGuess substringWithRange:range]];
    [list addObject:string];
}

I’ve made sure to check if self.equationToGuess always contains an equation using the debugger, and it does. list is also able to get some of the objects, but the problem is that it just puts the last two characters in one shelf on the list. So if I have that “3x+4” equation, this chunk of code puts “3”, “x”, and “+4” into the code, and then it crashes because it goes beyond the length of the string. Does anyone know how to fix this?

Answer 1

Let’s do this with a bit more panache:

NSInteger numberOfCharacters = [self.equationToGuess length];
NSMutableArray *characterArray = [[NSMutableArray alloc] initWithCapacity:numberOfCharacters];
for (NSUInteger idx = 0; idx < numberOfCharacters; idx++) {
    NSRange range = NSMakeRange(idx, 1);
    [characterArray addObject:[self.equationToGuess substringWithRange:range]];
}

Edit

After a hearty helping of humble pie – this is still not the best way to do it: if your equation has multi-digit coefficients, they will be split up. Have you considered using NSScanner to split the string up instead?