XCode How to evaluate String formula with an X expression inside

Question

I\'m tring to evaluate a string formula to a float but, I cannot find a solution. Here is an example. I need to calculate about 200 formulas in this way.

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Answer 1

You should do as following:

1. Substitute x with its value in the string\
2. Take operands (values) and operators into the stack in the Reverse Polish Notation
3. Perform calculations
4. Return result

This is how I would to that.

Answer 2

Swifty Answer,

let formula = "12.845*x+(-0.505940)"
let x = 12

let expr = NSExpression(format: formula)
let object = ["x":x]

let result = expr.expressionValue(with: object, context: nil)

print(result)
//Output: 153.63406

Answer 3

You can use NSExpression:

NSString *formula = @"12.845*x+(-0.505940)";
float x = 12.0;

NSExpression *expr = [NSExpression expressionWithFormat:formula];
NSDictionary *object = [NSDictionary dictionaryWithObjectsAndKeys:
                          [NSNumber numberWithFloat:x], @"x", nil];

float result = [[expr expressionValueWithObject:object context:nil] floatValue];
NSLog(@"%f", result);
// Output: 153.634064

This works even with some functions such as sqrt, exp, ... See the NSExpression documentation for a list of supported function.