Hello! How we can compute strings in swift. For example, "5*4-1+3"

Like this:

let expression = NSExpression(format:"5*4-1+3")
let value = expression.expressionValue(with: nil, context: nil) as? Int

value returned will be an Optional Int

See much more that can be done with NSExpression here: NSExpression - NSHipster (though be warned that it's several years old and some of the functions have since been renamed)

Thank you, but I got 6 as a result for this expression "2x3-1/5" . it shuld be 1. for example: "2x3" = 6 ; "6-1" = 5 ; "5/5" = 1

I got 6 as a result for this expression "2x3-1/5" . it shuld be 1. for example: "2x3" = 6 ; "6-1" = 5 ; "5/5" = 1

I think it's because 1/5 is being interpreted as a fraction. 2*3 = 6 then it is subtracting 1/5. But since the answer is an Int, it's coming out as 6.

If you use parentheses to properly indicate precedence, it will give you the correct answer:

"(2*3-1)/5"

The answer to "2 * 3 - 1 / 5" equal 5.8 there as Int would display 6 because times multiple and division are done first before addition and subtraction.

2 multiple 3 equal 6

1 divided 5 equal 0.2

6 minus 0.2 equal 5.8

as typecast to Int would round to nearest whole number as 6

if you want answer one do "(2 * 3 - 1) / 5" equal 1

when I applied let expression = NSExpression(format:formula) I got "(2 * 3) - (1 / 5)", this variable (formula) is not fixed as "2 * 3 - 1 / 5" it is jus example for many expression styles

thnk you

NSExpression - NSHipster describes several other ways to use NSExpression. I am not understanding how to use sttdev or more interestingly modulus calculations. Any assistance?

My feeble attempt:

 let expn = NSExpression(forFunction: "modulus:",
                        arguments:[NSExpression(modulus: "10", by:"5")])
print (expn)
let valueForOperand = expn.expressionValue(with: nil, context: nil) as? Int
print (valueForOperand!)

Change:

let expn = NSExpression(forFunction: "modulus:",
                        arguments:[NSExpression(modulus: "10", by:"5")])

to:

let expn = NSExpression(forFunction: "modulus:by:",
                        arguments:[
                            NSExpression(forConstantValue: 10),
                            NSExpression(forConstantValue: 5)
                        ])

You can see what arguments each funnction takes here.