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‫Instructor: Hi.

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‫Within this lecture, we are going to define the views

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‫into our view controller

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‫and then, we're going to work on them.

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‫So let me add a new editor over here

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‫and you can click on this view controller

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‫to bring view controller on the right hand side.

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‫Or remember, you can choose the viewController.swift

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‫from here as well.

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‫So, this is the same thing.

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‫And in the left hand side,

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‫we already see the main storyboard.

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‫So, all we have to do is click drag and drop the view.

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‫So, remember you have to press control in your keyboard

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‫and then drag and drop inside of the class,

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‫but outside of this function.

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‫So inside of this class, I'm going to call this

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‫"firstNumber" or "firstTextNumber", okay?

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‫I'm going to call this "firstText."

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‫I believe this is the simplest thing that I can call.

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‫So this is "firstText."

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‫Let me add some couple of more lines,

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‫and I'm going to bring in

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‫the "secondText."

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‫So this is "secondText."

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‫Okay?

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‫So let's say, "Connect",

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‫and then, I believe we have to bring our label

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‫and then, our buttons as well.

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‫Remember, if you made a mistake,

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‫you can break the connections over here

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‫and delete everything and redefine,

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‫but if not, just don't go with it.

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‫So I'm going to need some more actions

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‫to connect to over here.

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‫But first I'm going to get my resultLabel.

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‫So let me bring this over here and call this "resultLabel."

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‫Okay, so we are done with the text fields labels.

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‫Now let's go for actions.

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‫So first will be my adding summation function.

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‫So let me

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‫try to take this and bring this over here

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‫and this is going to be an action,

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‫and let's call this something like "someAction"

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‫or "someButtonClicked", okay?

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‫Let's call it "someClicked"

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‫and connect to our view controller.

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‫So we have our first action, let's go for others.

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‫So, the second one will be deduction.

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‫So I'm going to call this "minusClicked."

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‫I'm not being consistent over here.

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‫One is "someClicked" and the second one is "minusClicked."

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‫Maybe I could have called it

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‫"deductionClicked" or something, but it doesn't matter.

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‫So third one will be "multiplyClicked."

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‫Okay?

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‫And we are here for the last one.

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‫Okay?

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‫So let's go for the last one,

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‫and drag and drop to our view controller.

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‫So I'm going to call this "divideClicked."

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‫So, let's call "divideClicked"

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‫and then connect.

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‫So here we go.

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‫We have defined everything in our view controller.

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‫So, we are now ready to go and write our code.

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‫So let me close this down and let me choose view controller

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‫and run this on my simulator

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‫to actually see how it looks like

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‫on a real phone or a real simulator screen, okay?

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‫It's wise to do that at this point

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‫because if you see any problem

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‫without going through all of the changes

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‫in the coding section,

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‫you may want to adjust the views a little bit

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‫and then continue writing your code.

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‫So let me

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‫bring this simulator up

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‫and see if we can get the result over here.

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‫And maybe we can just take a look

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‫at the simulator's headings as well

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‫because we have seen how to run the simulator,

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‫but we haven't seen the settings

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‫of the simulator here as well because they,

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‫simulators have their own settings,

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‫and then you click on a simulator, you can reach their menu.

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‫Okay?

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‫So these are two different kind of softwares

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‫and they have their own menus,

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‫so you can access them from here.

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‫So we see our app, we click on first number for example,

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‫and we can try to write something.

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‫Yeah, it'll write.

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‫So everything seems to be in order.

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‫And let me show you what I mean by settings.

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‫If you go to debug section over here, for example,

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‫you can see some location or,

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‫if you go to hardware, you can see the keyboard.

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‫So maybe you can just say, "Toggle software keyboard",

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‫and it will pop up the keyboard for you, okay?

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‫So you can type it from here as well.

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‫Generally, developers don't like to use it that way,

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‫so they can type it from their own keyboard,

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‫but you can change the settings

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‫from this keyboard menu as well.

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‫So, you can do whatever you want with this simulator.

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‫You can change its location, you can change its name.

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‫So this is a great tool and as you can see,

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‫nothing happens as I click on these buttons

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‫because I haven't written them yet.

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‫So let's stop this and go to viewController.swift,

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‫in which where we are going to write our codes.

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‫So we are going to start with the sumClicked.

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‫We are going to test the first function and if that works,

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‫we're going to reapply the same techniques

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‫to other functions as well.

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‫So what do I wanna do in the sumClicked?

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‫First I want to get the first number, right,

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‫and then I want to get the secondNumber,

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‫and I want to display the result

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‫of their summation together in the resultLabel.

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‫So let me create firstNumber variable.

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‫So the first number will be firstText, right?

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‫So this will be the place, this will be the view

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‫that our user is going to be writing their inputs.

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‫So I'm going to say, "firstText.text."

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‫So if you just look at the attributes and methods over here,

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‫you will see something like text.

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‫So this is the text displayed by the text field.

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‫So whatever has our user written in this text field,

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‫we can get it by saying, "firstText.text."

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‫So this is cool, we already got

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‫what is written inside of the first text,

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‫but this is going to be an string,

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‫it's not gonna be an integer.

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‫Okay?

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‫So we just got this "firstText.text",

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‫and it doesn't make sense to add this string to another.

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‫We have to convert this to,

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‫into an integer or a double in order to make the same thing

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‫with the secondText and they sum it up together.

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‫So wrap this around an integer

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‫and this will convert this text into an integer.

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‫What is the problem here?

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‫So we have

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‫to force cast this or we have to provide

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‫a double question mark in our in order to make this optional

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‫and provide a default value as you might remember.

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‫So I'm going to force unwrap this first.

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‫I will try and see if that works with force unwrapping.

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‫If that works, very good,

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‫if that doesn't, I will change it.

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‫Okay?

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‫I'm going to do the same thing for secondNumber as well.

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‫So I'm going to say, "Let's secondNumber

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‫is going to be the integer

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‫of secondText.text", okay?

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‫Int secondText.text.

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‫So that's okay.

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‫And, we are going to sum this two together

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‫and we still haven't done yet.

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‫So we have to force unwrap this one more time.

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‫I'm going to show you why.

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‫I'm going to create another value over here,

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‫I'm going to call this "result."

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‫This is going to be the integer.

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‫This is going to be firstNumber plus secondNumber, right?

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‫So this is first number,

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‫but we see, this is integer optional,

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‫so this isn't good.

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‫So secondNumber is integer optional as well.

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‫And guess what, we cannot do that

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‫because the binary operator of summation,

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‫binary operator of summing these two numbers together

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‫cannot be applied to integer optionals,

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‫so we have force unwrapped this.

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‫Why it is an optional?

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‫Because right now, the first exclamation point

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‫only stands for firstText.text is going to be a text,

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‫we are certain of that.

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‫And if we put another exclamation point over here,

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‫it means that this is definitely going to be an integer.

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‫So as you can see now, this doesn't give me any error,

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‫because the first number is not an integer optional anymore.

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‫So let me tell you one more time,

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‫the first exclamation point means that this firstText.text

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‫is going to be definitely over there.

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‫And we know that even if user doesn't give an input,

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‫we are going to get a string from there, right,

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‫an empty string, we are not going to get a nil value,

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‫we are certain of that.

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‫So this is,

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‫over here, we are certain that firstText is defined

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‫and it's not going to return us a nil value, it's going to,

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‫at the worse, it's going to return us an empty string.

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‫And we are making certain of that

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‫by putting this exclamation point in this stage.

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‫And if we add the other one, if we add the second one,

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‫it means that we are certain that

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‫we are definitely going to convert it into an integer.

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‫Let's see if we delete this,

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‫and if I come over here and if I write firstNumber,

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‫it will make this integer an optional integer, okay?

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‫And this is okay for Xcode, this is optional.

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‫But if I put this, this is going to be, and not optional,

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‫this is going to be a regular integer.

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‫And by this time we are betting, we are saying

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‫that this is definitely going to be a string

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‫and this string is definitely going

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‫to be converted into integer.

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‫And later on, I can just take this resultLabel

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‫and I can say, "resultLabel.text

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‫is now result."

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‫Okay?

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‫But I cannot say that because resultLabel.text

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‫is expecting a string from me

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‫and I'm giving an integer to it, right?

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‫So I have to convert this into a string.

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‫So I can just go like this, string result.

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‫So this will convert result into a string

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‫and I can definitely do that, once I got the result,

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‫I can definitely make an integer into a text, right?

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‫This is going to be okay anyway.

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‫So let me run this and let's see if this works.

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‫So we are gonna get the firstText.

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‫So let me give this something like 40 or, five.

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‫So let me give this 10, let me just sum them together,

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‫and here we go, the 15.

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‫So let me give minus 10 and minus five.

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‫So let me give a big number,

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‫and let me give a very big number.

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‫So that's still working and it doesn't seem to be crashing,

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‫but if I come over here and say, "Apple", okay,

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‫and if I want to sum them together,

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‫as you can see, it crashed.

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‫So, this is definitely going to be this way

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‫because as you can see it says

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‫that it is unexpectedly found nil

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‫while unwrapping an optional.

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‫So we have said that this is definitely

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‫going to be over there, but it's not there.

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‫We couldn't even convert this to be an integer.

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‫So since this integer is not there,

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‫since this in integer is a nil,

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‫the application crashed.

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‫And the good thing is,

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‫you know how to make this safe, right?

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‫You know what to do in a a situation like this.

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‫Of course you can go with double question marks

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‫or you can go with default values, but we do not want that.

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‫We just want

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‫to have a safe number and have a safe calculation,

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‫so that even if the user doesn't give the right input,

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‫we would not crash the app

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‫and we would get the result that we want.

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‫We are gonna do that in the next lecture.