Two Problems in Swift

Question

I am new to programming and I am making my first app in xcode. I keep getting these 2 errors with little to no information on them on the internet. They are as follows:

Binary operator '*' cannot be applied to operands type '_' and 'String'"

Binary operator '*' cannot be applied to two 'String' operands.

This is the code I have for it.

@IBAction func Calculate(_ sender: UIButton){

    // V_1 = (M_3V_2-M_2V_2)/(M_1-M_3)

        var a = CurrentPH.text
        var b = TargetPH.text
        var c = WaterVolume.text
        var d = PHDownn.text
        
        var Answer = b! * c! - a! * c! / d! - b!
        Answer = PHOutput.text
    }
}

Answer 1

Read about binary operators, they need 2 operands to work with. Such as multiplication.

You cannot apply * (multiplication) on two strings.

The first error says that You cannot multiply [anything] with String and the second that you cannot multiply 2 strings together.

It's not clear from your question what are you trying to do.

Answer 2

Adding to what @DeepBlue is saying, I believe what you are trying to do, is to calculate with the values from text fields and place the answer in a fifth text field, when you press a button.

That would look something like this

@IBAction func Calculate(_ sender: UIButton){

    // V_1 = (M_3V_2-M_2V_2)/(M_1-M_3)

        let a = Int(CurrentPH.text!)!
        let b = Int(TargetPH.text!)!
        let c = Int(WaterVolume.text!)!
        let d = Int(PHDownn.text!)!
        
        let answer = b * c - a * c / d - b
        PHOutput.text = String(answer)
    }
}

Since none of the variables are modified, I'm using let instead which makes them constants.

Since converting a String to an Int can fail, for example if you type text into the text fields, it can result in a nil result. To simplify the formula the integer conversion is force unwrapped.