Is there a function that translates a string into math equation?

[Cori]

Hi, I'm new to Objective-C and I'm looking for a way to do a quick arithmetic operation given a specific equation, in string.

For example:
NSString *eq1 = @"10+20-30*40/50";
NSString *eq2 = @"(10+20)-30*40/50";

double total = MATH_FUNCTION(eq1) + MATH_FUNCTION(eq2);

Is there a MATH_FUNCTION that can translate a string into a math equation? And also apply the arithmetic rules of MDAS when processing the operands inside the string?

Thanks for reading and answering!! :-)

[mokargas]

Originally Posted by Cori

Hi, I'm new to Objective-C and I'm looking for a way to do a quick arithmetic operation given a specific equation, in string.

For example:
NSString *eq1 = @"10+20-30*40/50";
NSString *eq2 = @"(10+20)-30*40/50";

double total = MATH_FUNCTION(eq1) + MATH_FUNCTION(eq2);

Is there a MATH_FUNCTION that can translate a string into a math equation? And also apply the arithmetic rules of MDAS when processing the operands inside the string?

Thanks for reading and answering!! :-)

iphone - NSString to equation - Stack Overflow

[Cori]

Thanks for helping, Mokargas! I like you!!

I was excited to find the NSPredicate solution but unfortunately, it yields wrong calculations when it's division and the dividend and divisor are both integers, for example:

NSString *str7 = @"((10+(25/22))*10)"; // shd be 111.36364, not 110
NSString *str8 = @"((10+(25/22))*10.111)"; // shd be 112.59977, not 111.221
NSString *str9 = @"((10+(25/22.0))*10.111)"; // the fix to get 112.59977

NSString *equation = @"1+5*6";
// dummy predicate that contains our expression
NSPredicate *pred = [NSPredicate predicateWithFormat:
[equation stringByAppendingString:@" == 42"]];
NSExpression *exp = [pred leftExpression];
NSNumber *result = [exp expressionValueWithObject:nil context:nil];
NSLog(@"%@", result); // logs "31"

Apparently the float result is always converted to integer. So for workaround, I replaced the string's occurrences of @"/" with @"*1.0/" though I'm not sure that is a reliable solution.

Few days ago I came across a short doc on Tcl Math Library, that mentioned a linear algebra pkg, like below:

This manual page is for Mac OS X version 10.6.6
…
…
math(n) Tcl Math Library
NAME
math - Tcl Math Library
SYNOPSIS
package require Tcl 8.2
package require math ?1.2.4?
//... text edited out…
• math::geometry - 2D geometrical computations
• math::interpolate - Various interpolation methods
• math::linearalgebra - Linear algebra package
• math::optimize - Optimization methods
//... text edited out…

The thing is I have no idea if I can use this Tcl math lib for an iPhone app, nor do I know how to find this lib. I'm also wondering it has a good docu about that linear algebra.