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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

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

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.

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
17,972 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

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