Are you adding a new file to the project and adding that code? If so, you have two main functions, giving you a Duplicate Symbol error. A C program can't have two main functions. Remove the main function in the main.c file that was created when you created the project. When you create a command-line tool project, Xcode provides a main.c file. Why are you creating another file instead of using the main function Xcode created for you.

The .h file is a header file. Most C files have an accompanying header file. If you create a command-line tool project and run it without adding any files, do you get the Duplicate Symbol error message? Show the code in the new C files you're creating. When I create a command-line C project, add a C file with a header, and run the project, the project builds and prints Hello, world to the console.

The deployment target is the earliest version of iOS that can run your app. If you set the deployment target to iOS 13.2, it will run on iOS 13.2 and above, including iOS 14. The problem you're going to run into using Xcode 11.3 on a device with newer iOS versions (newer than iOS 13.2 for Xcode 11.3) is you won't be able to debug on the device. But this limitation hasn't stopped you with your device running iOS 13.5 so things wouldn't change updating to iOS 14.

For anyone to help you, you need to provide more information. List the steps you take to create the Xcode project. What kind of Xcode project did you make? If you create a command-line tool project and run it, do you get the Duplicate Symbol error message? List anything else you do before building the project, such as any files you added to the project. A common cause of a Duplicate Symbol error message in a C project is to create a command-line tool project, add a new file, and add a main function to the new file. The project comes with its own main function so you end up with two main functions. A C program can have only one main function.

Do I have to program the app for each Iphone separately No you don't. how could I make it so that the labels and texts (no matter how big the Iphone is) are in one uniform place? If you are using UIKit for the app's user interface, do some research on auto layout. Apple provides an Auto Layout Guide - https://developer.apple.com/library/archive/documentation/UserExperience/Conceptual/AutolayoutPG/index.html#//apple_ref/doc/uid/TP40010853-CH7-SW1 on their developer website. If you are using SwiftUI, you declare how you want the interface to look, and SwiftUI takes care of the details.

Creating a theme is how you set a font for the text in Xcode. I'm not sure if Xcode supports custom fonts, but take the following steps to create a theme and set a font: Choose Xcode Preferences. Click the Themes button at the top of the preferences window. Select one of the themes that you want to duplicate. Click the Add button below the list of themes. Choose Duplicate from the menu of theme choices. Select your duplicated theme and press the Return key to rename the theme. Select all the items for the theme, starting with Plain Text and ending with the last item, which should be Heading. Below the list of items is a selected font. Next to the font is a small button. Click that button to open the Font panel and choose the font.

Make sure the saveContext function is called by setting a breakpoint on that line of code. Does it get called in applicationWillTerminate? I made a mistake in my first reply. For an iOS app the function where you should save the context is applicationDidEnterBackground. That's the function that will be called when someone quits the app. The applicationWillTerminate function does not get called until the app is purged from memory completely, which requires the user to launch several apps after quitting your app. Can you explain what you mean by "make the object persistent"? Saving the context is how you save data in Core Data.

To save when the app exits, go to the AppDelegate.swift file. For an iOS app there will be a function called applicationWillResignActive. In a Mac app, the function will be called applicationWillTerminate. These functions are called when quitting the app. Call the saveContext function in either applicationWillResignActive or applicationWillTerminate.

Create an Objective-C command line tool project. Choose Command Line Tool from the list of Mac app project templates. Click the Next button. Choose Objective-C from the Language menu.

You can set the delegate from the storyboard instead of in the viewDidLoad function. In the storyboard, make a connection from the text field to the view controller and choose the delegate outlet. If that does not work, you should tell us the book you're following. The following article provides a detailed explanation of the error message you are getting: swiftdevjournal.com/crashing-with-swift-optionals/

If you option-click the Add button in the project window toolbar, the Library window will stay open. I don't know if that's what you mean by "pin the library view on the Xcode desktop", but if option-clicking isn't enough for you, you will have to explain what you mean by pinning the library view.

If you are stuck on High Sierra, you cannot learn SwiftUI. Either learn UIKit for iOS development or AppKit (Cocoa) for Mac development. You will not be able to submit iOS apps to the App Store with Xcode 10, but you can use Xcode 10 to learn iOS development. The following articles provide resources for learning iOS and Mac development, most of which do not use SwiftUI: swiftdevjournal.com/learning-ios-development/ swiftdevjournal.com/resources-for-learning-mac-development/ Unforunately these forums don't let us add clickable links so you will have to copy and paste the URLs in your browser.

There is no Xcode beta available for Catalina. Just use Xcode 12.4, which you can download from the App Store or from Apple's developer downloads page. If you can't find Apple's developer downloads page, the site Xcode Releases (xcodereleases.com) has Apple's download links for every Xcode version.

For an iOS app deleting the app and reinstalling it will trash the existing data. For a Mac app, the Core Data store is in the Application Support folder. For a Core Data app of mine, the file has the extension .storedata. Move the store file to the Trash to delete it.

If by versioning you mean creating a new version of the Core Data model, create a new version of the data model when you reach the point in development that you want to keep the existing data in your app. In the early stages of making your app it's easier to trash the existing Core Data store (file) and starting with a fresh store. Eventually you will hit a point where starting with a fresh store causes problems, such as when other people start using your app. That's when you need to create a new version of the model and migrate from the old version to the new version.