CODEWITHSUNDEEP
iphoneobjective-ciosparsingexpression
Alex Stone
Alex Stone

Reputation: 47348

iPhone iOS is there an expression parser for an algebraic calculator-like app?

I'm building an app that would analyze phone's motion through accelerometer and gyroscope output. It is likely that I will capture this motion as a set of variables that the app would keep track of internally.

I'm trying to include a way to graph these variables and equations involving these variables. I would like to offer the user an ability to adjust how the app displays equations of these variables by typing equations like a + b - c = d with the a,b,c variables being calculated by my app. The user can write equations and graph variables in the field. Since it has been ages since I wrote an algebraic parser in any language, I'm wandering if there's an expression parser in objective-c that I can readily plug into my app, where a user would type something like a + b - c = d into a text field and the app would tokenize and substitute variables that I provide in place of the user-entered placeholders.

Upvotes: 2

Views: 1458

Answers (2)

AntonTheDev
AntonTheDev

Reputation: 919

There is a much easier approach to do this :) Check out the NSExpression foundation class. It is the same class used when you type an expression into the spotlight.

NSExpression Class Reference

In Objective-C

NSExpression *expression = [NSExpression expressionWithFormat:@"2*4*3" argumentArray:nil];
NSNumber *result = [expression expressionValueWithObject:nil context:nil];

In Swift

var expression:NSExpression = NSExpression(format: "4 + (3 * 2)", argumentArray: [])
var result = expression.expressionValueWithObject(nil, context: nil)

Upvotes: 1

PaulPerry
PaulPerry

Reputation: 906

A couple of open source options:

GCMathParser http://www.apptree.net/parser.htm

DDMathParser https://github.com/davedelong/DDMathParser

Upvotes: 4

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