writing my first function without help... but now I need help

Ok, I expanded on your function a bit (or quite a bit) to try and demonstrate when we want to return something and when we don't. So here we go:

//: Playground - noun: a place where people can play

import UIKit

var todoList: [String: String] = ["Monday": "Take out garbage", "Tuesday": "Study",
                                  "Wednesday": "Clean room", "Thursday": "Call parents",
                                  "Friday": "Do finances", "Sunday": "Cook for the week"]

func add(toDay x: String, withTask y: String) {  // No return is needed here at all

    todoList.updateValue(y, forKey: x)
    print(todoList)

}

func displayList() {
    for (day, task) in todoList {
        print("\(day):  \(task)")
    }
}

func doToday(for day: String) -> String {  // a return is needed here
    return todoList[day]!  // This going to return the task that was found at the day that we ask for
}

add(toDay: "Saturday", withTask: "Iron your bed")
displayList()
print()
print("I need to do this today: \(doToday(for: "Wednesday"))")  // we search for a day and print the value returned to us

To fix your original code, all was needed was to erase the -> String. You didn't need to return a string as you were printing the list from right there. In fact, you didn't need to return anything. But if you tell a function you're going to return a String or int or any other data type, then it will absolutely demand that you do so. You could have also fixed it by returning any arbitrary string such as return "Hello World", but that "Hello World" would never have been visible anywhere.

I added a function to display the list to help differentiate the difference between keys and their values. The for loop goes through each pair and prints out the key and the value. The key is your day, and the value is the task you need to do.

I also included a print statement at the bottom. This print statement calls another function (which is also fairly unnecessary but serves to demonstrate what I mean) that passes the day into a function which returns what you're supposed to do on a particular day. I picked the day "Wednesday". At this point, the function executes and gets the task value located at the key "Wednesday". That value (a string) is then returned to the print statement that called it. The returned string is then inserted into the string interpolation and printed out with the rest.

Hope this helps!

Thanks for your help! That all makes sense, except for one thing. I thought my dictionary had been defined as a string. So when I print it, I thought it was showing a string. At one point, within the function, I wrote return todoList but I got the same error as above.

So I guess the two questions still remain: -Why isn't my dictionary a string? -Could you help me better understand the difference between print and return and the importance of the latter?

Thanks again for your help.

For the dictionary part, I understand that now. Apart from not returning anything (which works now), what could I have returned to make the function work? I tried all sorts of things but to no avail, FYI.

So for the return comment, the function basically performs the task (opening jar) and by returning it (handing back the jar) to the beginning of the function (where it was called) so that you could do other things with it, like make dinner. In that analogy, where would the return value be passed to make dinner? Because what's returned might not be able to pass through it again if, say, the function requires two arguments and but you're only returning one. So would the jar be passed through another function (or some other piece of code)?

Drawing off that analogy, say I fixed the return issue with my function and added another key and value to my dictionary. Once it's returned, where else would that information go/be used?

Also, yes. Example code would be helpful.

Yes, that's super helpful!

I understand your answer to my original code. And I understand the displayList takes a pass through the dictionary and returns its key: value. I also understand the code in the last four lines. However, I'm getting tripped up by the following:

func doToday(for day: String) -> String { // a return is needed here return todoList[day]! // This going to return the task that was found at the day that we ask for }

I understand the concept behind the code and what it does, but from everything I've learned this far I haven't seen it represented this way before. Could you explain how it knows to get the value of the key without using forKey? Is for day the same as forKey but you can replace Key with anything you want and add space?

Also, what's the purpose of ! ? I've seen it used as != and know what that means, but not when it comes at the end.

And one more question. When I write functions, arrays, dictionaries, switch statements, etc. it takes me quite a bit of time, as I have to think really hard and reference my notes to make sure I'm doing it properly and understanding the logic. (trial and error helps too) But I want to get quicker, hence Pasan's comment about practicing the writing of several functions, etc. before moving on. That said, are there sites that have basic drills like this where I can pound it through my head with lots of repetition?

No, I haven't gotten to optionals yet. Thank you for your thoughtful responses. Been really helpful, and I will definitely work on pacing myself. :)