COMP 1601 2021W Assignment 1 Solutions

1.  Replace lines 46-48 of ContentView.swift with the following:

            if let from = Double(fromString) {
                if let to = conv.convert(from) {
                    Text("\(fromString) \(conv.convFrom) is ") +
                        Text("\(to) \(conv.convTo).").bold()
                } else {
                    Text("Conversion failed.")
                }
            }

     Note we couldn't use formatConversion(); instead we called
     convert() directly and generated the string ourselves, bolding
     only part of the text as shown in Tutorial 1.

2a. Replace the for loop on lines 7-9 with the following:

       var i = 0
       convAvail.forEach({c in
           i = i+1
           print(" \(i). \(c)")
       })

     Note how we have to manually create a loop index using a variable
     declared outside of the forEach closure.

2b. Change line 22 from:

          let getConversion = {(_ choice: String) in

      to:

          func getConversion(_ choice: String) {

2c. The function getConversion should be changed as follows.  One line
      is changed and two are added, but most of the body gets
      re-indented.  Note that the added print statement would only run
      if an unknown choice is given.  With the way this program is
      constructed this could never happen; however, later changes
      could result in an undefined choice.

func getConversion(_ choice: String) {
    if let conv = conversions[choice] {       // <--- added an if here and {
        print("\nEnter \(conv.convFrom): ", terminator: "")
        if let vs = readLine() {
            if let v = Double(vs) {
                let res = conv.formatConversion(v)
                print(res)
                return
            } else {  // <--- added an else
                print("You didn't enter a number!") // <--- added this print
            }
        }
    } else {
        print("Unknown conversion \(choice)!")
    }
}

2d. First, add a new menu item at the end by inserting this after
      printing the menu (line 10):

          print(" \(convAvail.count + 1). Quit")

      Next, return "Quit" when this option is selected (insert between 16 and 17):

          print(" \(convAvail.count + 1). Quit")

      Finally, add a while loop to the last part of the program.
      Replace lines 36-40 with the following:

         var done = false
         while !done {
             if let choice = getChoice() {
                 if choice != "Quit" {
                     getConversion(choice)
                     print("")
                 } else {
                     print("Goodbye!")
                     done = true
                 }
             } else {
                 print("You didn't make a valid choice!")
             }
         }

3a. First, add a new property to the Converter struct at Conversions:7:

         var defaultVal: String

      Then, change init as follows (Conversions, 16-20):

         init(_ from: String, _ to: String, _ f: @escaping (_ from: Double) -> Double?,
	      _ d: String) {   // <--- added to function declaration
             self.convFrom = from
             self.convTo = to
             self.convert = f
             self.defaultVal = d  // <--- added
         }

      Finally, add the default values to the conversions (replacing lines 28-40):

let conversions: [String: Converter] =
    ["F to C": Converter("Farenheit", "Celsius",
                         {F in return ((F - 32.0)*(5/9))}, "32.0"),
     "C to F": Converter("Celsius", "Farenheit",
                         {C in return ((9/5)*C + 32.0)}, "0.0"),
     "km to mi": Converter("kilometers", "miles",
                           {k in
                            let m = k * 0.6213712
                            return m
                           }, "88.0"),
     "inch to cm": Converter("inches", "centimeters",
                             InToCM, "12.0")
    ]


3b. Replace ContentView:31 with the following:

                    if let c = conversions[conversion] {
                        fromString = c.defaultVal
                    } else {
                        fromString = ""
                    }

3c. Add a new view (around ContentView:55):

struct ConvPrompt: View {
    @Binding var convMode: String?
    @Binding var fromString: String

    var body: some View {
        if let c = convMode {
            if let conv = conversions[c] {
                if conv.defaultVal == fromString {
                    Text("Please enter your own number to convert.").italic()
                }
            }
        }
    }
}

   To add this view, add the following between ContentView:15 and 16
   (between the calls to Spacer):

            ConvPrompt(convMode: $convMode,
                       fromString: $fromS)
 
3d. The message disappears the moment one character is entered or
      changed.  This means that the new view has to be run on every
      keypress and every time a new menu item is selected.