Int() 不会从 String 转换为 Optional Integer (Swift)

Question

I'm new at programming and started with Swift. The first issue I came along with is the following:

I have 4 variables

var a = "345"

var b = "30.6"

var c = "74hf2"

var d = "5"

I need to count the sum of Integers (if not integer, it will turn to nil)

if Int(a) != nil {
  var aNum = Int(ar)!
} 

if Int (b) != nil {
  var bNum = Int (b)! 
}       

and so on..

As far as I understand, the Int() should convert each element into an Optional Integer.

Then I should use forced unwrapping by convertin the Int? to Int and only then I can use it for my purposes. But instead, when I count the sum of my variables, the compiler sums them as Strings.

 var sum = aNum + bNum + cNum + dNum

Output:

  34530.674hf25

Why my variables, which are declared as strings and then converted into optional integers with Int(), didn't work?

Answer 1

Your code has typos that make it hard to tell what you are actually trying to do:

Assuming your 2nd variable should be b , as below:

var a = "345"
var b = "30.6"
var c = "74hf2"
var d = "5"

///Then you can use code like this:

var sum = 0

if let aVal = Int(a) { sum += aVal }

if let bVal = Int(b) { sum += bVal }

if let cVal = Int(c) { sum += cVal }

if let dVal = Int(d) { sum += dVal }

print(sum)

That prints 350 since only 345 and 5 are valid Int values.