Solving math using DDMathParser in Objective-C

Question

I'd like to use DDMathParser to solve a math problem. The top answer on this StackOverflow question shows how, but it only solves it to the log. I'd like to get the answer as a string on an integer. The code NSLog(@"%@", [math numberByEvaluatingString]); also works, but it only prints it to the log.

What I'd like to do would be something like answerText = @"%@", [math numberByEvaluatingString];, where "math" is the string to evaluate, and "answerText" is the string to push the answer to. However, when I try to display the string in a label like Label.text = [NSString stringWithFormat:answerText];, I get a sigabrt error. I'm not sure what's up. That code does not work at all with an integer.

Thanks in advance!

Answer 1

Try:

label.text = [NSString stringWithFormat:@"%@", [math numberByEvaluatingString]];

There is probably a better way to coerce it to a string, but I'm too lazy to go see what numberByEvaluatingString actually returns.

Answer 2

The Objective-C version of DDMathParser returns an NSNumber. That means that in order to show it as the value in a textfield, you need to convert it to a string.

While using +stringWithFormat: would work, it's not technically correct. By using +stringWithFormat:, you're relying on the -description of the NSNumber, which may have information you don't want, or lack information that you do want.

The best way to "render" an NSNumber into an NSString suitable for human consumption is to use an NSNumberFormatter.