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iOS Swift 2.0 Collections and Control Flow Control Flow With Conditional Statements Working with Switch Statements

Ahmet GULER
Ahmet GULER
7,181 Points
Posted by Ahmet GULER
Ahmet GULER
7,181 Points

error: value of optional type 'String?' not unwrapped

i am trying the challenge: https://teamtreehouse.com/library/swift-20-collections-and-control-flow/control-flow-with-conditional-statements/working-with-switch-statements

i am getting the following error : error: expression pattern of type 'String' cannot match values of type 'String?' case "BEL": europeanCapitals.append(world[key])

error: value of optional type 'String?' not unwrapped; did you mean to use '!' or '?'?

switch.swift 
var europeanCapitals: [String] = []
var asianCapitals: [String] = []
var otherCapitals: [String] = []

let world = [
  "BEL": "Brussels", 
  "LIE": "Vaduz", 
  "BGR": "Sofia", 
  "USA": "Washington D.C.", 
  "MEX": "Mexico City", 
  "BRA": "Brasilia", 
  "IND": "New Delhi", 
  "VNM": "Hanoi"]

for (key, value) in world {
    // Enter your code below
        switch world [key] {
       case "BEL": europeanCapitals.append(world[key])
       case "LIE": europeanCapitals.append(world[key])
       case "BGR": europeanCapitals.append(world[key])
       case "USA": otherCapitals.append(world[key])
       case "MEX": otherCapitals.append(world[key])
       case "BRA": europeanCapitals.append(world[key])
       case "IND": otherCapitals.append(world[key])
       case "VNM": asianCapitals.append(world[key])
    }
    // End code
}

3 Answers

Steve Hunter
Steve Hunter
57,712 Points

Hi Ahmet,

You want to be swtiching on the key and appending the value associated with that key.

The for loop provides you with each key/value pair one at a time, you then switch on the key. You can also combine multiple cases rather than coding each one, which is repetitive:

    switch key {
      case "LIE", "BEL", "BGR": europeanCapitals.append(value)
      case "IND", "VNM":  asianCapitals.append(value)
      case "BRA", "MEX", "USA": otherCapitals.append(value)
      default: break
    }

You could use the last set of cases in the default, I guess, but you see the idea!

I hope that helps,

Steve.

Steve Hunter
Steve Hunter
57,712 Points

Something like:

switch key{
      case "BGR", "BEL", "LIE": europeanCapitals.append(value)
      case "IND", "VNM": asianCapitals.append(value)
      default: otherCapitals.append(value)
 }
Zach Swift
Zach Swift
17,984 Points
Zach Swift
Zach Swift
17,984 Points

Just at first glance, I noticed you weren't using the "default" for other countries. I'm not sure off the top of my head if that's required.

Also, not related to the error, I noticed yu are appening to the list like .append(world[key]) When you already have acces to "value" inside the loop so you could do .append(value).

I'll have more time to loo at this a little later.

Ahmet GULER
Ahmet GULER
7,181 Points
Ahmet GULER
Ahmet GULER
7,181 Points

Hello,

yes as you have mentioned, when i replaced the statement 'switch world [key]' with 'switch key' the problem was solved.

And thanks for the nice tips

Best Regards,

Ahmet