Cannot invoke initializer for type 'Double' with an argument list of type '(String?)'

Question

I have two issues:

let amount:String? = amountTF.text

1. amount?.characters.count <= 0

It\'s giving error

Answer 1

amount?.count <= 0 here amount is optional. You have to make sure it not nil.

let amount:String? = amountTF.text
if let amountValue = amount, amountValue.count <= 0 {

}

amountValue.count <= 0 will only be called if amount is not nil.

Same issue for this let am = Double(amount). amount is optional.

if let amountValue = amount, let am = Double(amountValue) {
       // am  
}