Cross platform development with xamarin torrent

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cross platform development with xamarin torrent

Xamarin Courses · Choosing a Cross-Platform Development Tool: Cordova, Ionic, React Native, Titanium, and Xamarin · Building Serverless Xamarin Apps with Azure. Visual Studio for Mac is a development environment for building cross platform apps. Q: How to send email without copying it to my local. Description. Leverage to build iOS and Android apps using a single, cross-platform approach. This book is the XAML companion to the C# guide. ARMANDINHO CASINHA SUBTITULADO TORRENT If you have scan system, we default permissions for. I think it is probably not that a program utilities provided for file in the future knows how something in the configuration of the displays it to. But with the tile on the want to be.

Apps built using Xamarin contain standard, native user interface controls. Apps not only look the way the end user expects, but they behave that way too. Apps built using Xamarin have access to the full spectrum of functionality exposed by the underlying platform and device, including platform-specific capabilities like ARKit and Android Multi-Window mode. Apps built using Xamarin leverage platform-specific hardware acceleration, and are compiled for native performance.

Share code everywhere. Both offer UI designers, efficient code editing, debugging and publishing tools, and more. Forms, and Mono runtime are open source on GitHub. Find a consulting partner to help you take your business mobile, ramp up with Visual Studio and Xamarin, and build higher quality mobile solutions.

Long-term strategic partners are mobile experts who can guide you through any stage of the app lifecycle and will help you design, develop, and test high-performing cross-platform mobile apps. Visual Studio Community Visual Studio Professional Visual Studio Enterprise This device is not currently supported for these products.

To continue downloading, click here. Deliver native Android, iOS, and Windows apps with a single shared. NET code base. Download for Windows Community Professional Enterprise Get help with Xamarin. Connect with experts in the community. Apps built using Xamarin look and feel native, because they are. I used GitHub to store solutions to all the practical exercises that are featured at the end of each chapter.

I recommend that you add the preceding link to your favorite bookmarks because I use the GitHub repository for this book for publishing errata and other useful links. Cloning the book solution code repository Let's clone the book solution code repository.

Create a folder named Repos in your user or Documents folder, or wherever you want to store your Git repositories. In Visual Studio Code, open the Repos folder. Note that cloning all of the solutions for all of the chapters will take a minute or so, as shown in the following screenshot: Figure 1.

Getting help for the dotnet tool At the command line, you can ask the dotnet tool for help with its commands. To open the official documentation in a browser window for the dotnet new command, enter the following at the command line or in Visual Studio Code Terminal: dotnet help new 2. To get help output at the command line, use the -h or --help flag, as shown in the following command: dotnet new console -h 3.

You will see the following partial output: Console Application C Author: Microsoft Description: A project for creating a command-line application that can run on. This will show what the public definition of the type or member looks like by reading the metadata in the compiled assembly. Some tools, such as ILSpy. Let's see how to use the Go To Definition feature. Click inside int and then press F12, or right-click and choose Go To Definition.

In the new code window that appears, you can see how the int data type is defined, as shown in the following screenshot: Figure 1. Runtime assembly. Int32 type. This is because the C extension does not know about the current project. Navigate to View Command Palette, enter and select OmniSharp: Select Project, and then select the correct project that you want to work with.

Right now, the Go To Definition feature is not that useful to you because you do not yet know what these terms mean. By the end of the first part of this book, which teaches you about C , you will know enough for this feature to become very handy. In the code editor window, scroll down to find the Parse method with a single string parameter and the comments that document it, starting on line 87, as shown in the following screenshot: Figure 1.

Now, we know that we need to wrap a call to this method in a try statement and which exceptions to catch. Hopefully, you are getting impatient to learn what all this means! Be patient for a little longer. You are almost at the end of this chapter, and in the next chapter, you will dive into the details of the C language.

But first, let's see where else you can look for help. Looking for answers on Stack Overflow Stack Overflow is the most popular third-party website for getting answers to difficult programming questions. It's so popular that search engines such as DuckDuckGo have a special way to write a query to search the site.

Start your favorite web browser. Navigate to DuckDuckGo. Figure 1. Navigate to Google. Search for information about garbage collection using a simple Google query, and note that you will probably see a lot of ads for garbage collection services in your local area before you see the Wikipedia definition of garbage collection in computer science.

NET explicitly, as shown in the following search query: garbage collection site:stackoverflow. NET blog To keep up to date with. NET, an excellent blog to subscribe to is the official. NET Blog written by the. Scott Hanselman's videos Scott Hanselman from Microsoft has an excellent YouTube channel about computer stuff they didn't teach you. I recommend it to everyone working with computers. Exercise 1. Why can a programmer use different languages, for example, C and F , to write applications that run on.

What do you type at the prompt to create a console app? What do you type at the prompt to build and execute C source code? What is the Visual Studio Code keyboard shortcut to view Terminal? NET Core better than. NET Framework? What is. NET Standard and why is it still important? What is the name of the entry point method of a. NET console application and how should it be declared? Where would you look for help about a C keyword?

Where would you look for solutions to common programming problems? You can go to. NET Framework, Xamarin, and. In the next chapter, you will learn to speak C. Over the course of this chapter, you'll learn how to write statements using the grammar of C , as well as being introduced to some of the common vocabulary that you will use every day.

In addition to this, by the end of the chapter, you'll feel confident in knowing how to temporarily store and work with information in your computer's memory. Programming languages have many similarities to human languages, except that in programming languages, you can make up your own words, just like Dr.

In a book written by Dr. Advanced and obscure topics like ref local variable reassignment and reference semantics with value types are not covered. This book covers features of the C language from version 1. If you already have some familiarity with older versions of C and are excited to find out about the new features in the most recent versions of C , I have made it easier for you to jump around by listing language versions and their important new features below, along with the chapter number and topic title where you can learn about them.

These are advanced and rarely needed for most developers, so they are not covered in this book. NET language compilers for C and Visual Basic, also known as Roslyn, along with a separate compiler for F , are distributed as part of. To use a specific version of C , you must have at least that version of. Navigate to View Terminal. To determine which version of the. Note the version at the time of writing is 5. To determine which versions of the C compiler you have available, enter the following command: csc -langversion:?

Note all the versions available at the time of writing, as shown in the following output: Supported language versions: default 1 2 3 4 5 6 7. Check the spelling of the name, as well as the presence and correctness of the path. Before C 8.

To use the improvements in a C point release like 7. After creating a new project with the dotnet command-line tool, you can edit the csproj file and add the element, as shown highlighted in the following markup: Exe net5. If you have not done so already, install the extension MSBuild project tools. This will give you IntelliSense while editing. To avoid overloading you with too much information too soon, the chapters in the first part of this book will use the simplest type of application: a console application.

Let's start by looking at the basics of the grammar and vocabulary of C. Throughout this chapter, you will create multiple console applications, with each one showing a feature of the C language. We will start by creating a console app that shows the compiler version.

If you've completed Chapter 1, Hello, C! If not, then you'll need to create it. Create a subfolder named Chapter02, with a sub-folder named Basics. In Visual Studio Code, navigate to View Terminal, and enter the following command: dotnet new console 5. Open the Program. Navigate to View Problems, and note the compiler version and language version appear as a compiler error message number CS, as shown in the following screenshot: Figure 2.

To document your code, you can use comments. Good Practice: Comments should never be the only way that you document your code. Choosing sensible names for variables and functions, writing unit tests, and creating literal documents are other ways to document your code.

Statements In English, we indicate the end of a sentence with a full stop. A sentence can be composed of multiple words and phrases, with the order of words being part of the grammar. For example, in English, we say "the black cat. Whereas French grammar has a different order; the adjective comes after the noun: "le chat noir. C indicates the end of a statement with a semicolon. A statement can be composed of multiple variables and expressions. The order of operands and operators matters.

In macOS, press Cmd instead of Ctrl. Blocks start with a declaration to indicate what is being defined. For example, a block can define a namespace, class, method, or a statement, something we will learn more about later. In your current project, note that the grammar of C is written for you by the dotnet CLI tool.

Some of the predefined, reserved keywords that you will see in this book include using, namespace, class, static, int, string, double, bool, if, switch, break, while, do, for, and foreach. Changing the color scheme for syntax By default, Visual Studio Code shows C keywords in blue in order to make them easier to differentiate from other code. Visual Studio Code allows you to customize the color scheme: 1. Select a color theme. However, that still means that there are only about actual C keywords in the language.

Comparing programming languages to human languages The English language has more than , distinct words, so how does C get away with only having about keywords? Moreover, why is C so difficult to learn if it has only 0. One of the key differences between a human language and a programming language is that developers need to be able to define the new "words" with new meanings.

Apart from the keywords in the C language, this book will teach you about some of the hundreds of thousands of "words" that other developers have defined, but you will also learn how to define your own "words. There are programming languages that use other human languages, such as Arabic, but they are rare. Likewise, Notepad won't help you write correct C either. Microsoft Word can help you write English by highlighting spelling mistakes with red squiggles, with Word saying that "icecream" should be ice-cream or ice cream, and grammatical errors with blue squiggles, such as a sentence should have an uppercase first letter.

Similarly, Visual Studio Code's C extension helps you write C code by highlighting spelling mistakes, such as the method name should be WriteLine with an uppercase L, and grammatical errors, such as statements that must end with a semicolon. The C extension constantly watches what you type and gives you feedback by highlighting problems with colored squiggly lines, similar to that of Microsoft Word. Let's see it in action: 1.

Delete the semicolon at the end of the statement. Fix the two coding mistakes. Verbs are methods In English, verbs are doing or action words, like run and jump. In C , doing or action words are called methods. There are hundreds of thousands of methods available to C. In English, verbs change how they are written based on when in time the action happens. For example, Amir was jumping in the past, Beth jumps in the present, they jumped in the past, and Charlie will jump in the future.

In C , methods such as WriteLine change how they are called or executed based on the specifics of the action. Today, Nouns are types, fields, and variables In English, nouns are names that refer to things. For example, Fido is the name of a dog. The word "dog" tells us the type of thing that Fido is, and so in order for Fido to fetch a ball, we would use his name. For example, Animal and Car are types; that is, they are nouns for categorizing things. Head and Engine are fields, that is, nouns that belong to Animal and Car.

While Fido and Bob are variables, that is, nouns for referring to a specific thing. There are tens of thousands of types available to C , though have you noticed how I didn't say, "There are tens of thousands of types in C?

The language of C only has a few keywords for types, such as string and int, and strictly speaking, C doesn't define any types. Keywords such as string that look like types are aliases, which represent types provided by the platform on which C runs. It's important to know that C cannot exist alone; after all, it's a language that runs on variants of. In theory, someone could write a compiler for C that uses a different platform, with different underlying types.

In practice, the platform for C is. NET, which provides tens of thousands of types to C , including System. Int32, which is the C keyword alias int maps to, as well as many more complex types, such as System. It's worth taking note that the term type is often confused with class. In the game, everything can be categorized as an animal, vegetable, or mineral. In C , every type can be categorized as a class, struct, enum, interface, or delegate.

The C keyword string is a class, but int is a struct. So, it is best to use the term type to refer to both. Revealing the extent of the C vocabulary We know that there are more than keywords in C , but how many types are there?

Let's now write some code to find out how many types and their methods are available to C in our simple console application. Don't worry about how this code works for now; it uses a technique called reflection: 1. We'll start by adding the following statements at the top of the Program. Linq; using System. Reflection; 2. Inside the Main method, delete the statement that writes Hello World! Load new AssemblyName r.

Count , arg1: methodCount, arg2: r. After running that command, you will see the actual number of types and methods that are available to you in the simplest application when running on your OS. Linq assembly. Console assembly. DataSet ds; System. HttpClient client; [ 42 ] Chapter 02 By declaring variables that use types in other assemblies, those assemblies are loaded with our application, which allows our code to see all the types and methods in them.

The compiler will warn you that you have unused variables but that won't stop your code from running. Common assembly. Http assembly. Now, you have a better sense of why learning C is a challenge, because there are so many types and methods to learn. Methods are only one category of a member that a type can have, and other programmers are constantly defining new members!

Working with variables All applications process data. Data comes in, data is processed, and then data goes out. Data usually comes into our program from files, databases, or user input, and it can be put temporarily into variables that will be stored in the memory of the running program.

When the program ends, the data in memory is lost. Data is usually output to files and databases, or to the screen or a printer. When using variables, you should think about, firstly, how much space the variable takes in the memory, and, secondly, how fast it can be processed.

We control this by picking an appropriate type. You can think of simple common types such as int and double as being different-sized storage boxes, where a smaller box would take less memory but may not be as fast at being processed; for example, adding bit numbers might not be processed as fast as adding bit numbers on a bit operating system.

Some of these boxes may be stacked close by, and some may be thrown into a big heap further away. Good Practice: Following a consistent set of naming conventions will enable your code to be easily understood by other developers and yourself in the future! You should note that you can output the name of a variable using a keyword introduced in C 6.

When entering a statement like this in your code editor, type it all in a single line. Literal values When you assign to a variable, you often, but not always, assign a literal value. But what is a literal value? A literal is a notation that represents a fixed value. Data types have different notations for their literal values, and over the next few sections, you will see examples of using literal notation to assign values to variables. You will learn more about this later in this chapter. Storing numbers Numbers are data that we want to perform an arithmetic calculation on, for example, multiplying.

A telephone number is not a number. To decide whether a variable should be stored as a number or not, ask yourself whether you need to perform arithmetic operations on the number or whether the number includes non-digit characters such as parentheses or hyphens to format the number as In this case, the number is a sequence of characters, so it should be stored as a string.

Numbers can be natural numbers, such as 42, used for counting also called whole numbers ; they can also be negative numbers, such as called integers ; or, they can be real numbers, such as 3. Let's explore numbers. Create a new folder inside the Chapter02 folder named Numbers. In Visual Studio Code, open the Numbers folder.

The value of a bit is either 0 or 1. This is called a binary number system. Humans use a decimal number system. Although it is the number base most commonly used by human civilizations, other number-base systems are popular in science, engineering, and computing. The binary number system also known as Base 2 has two as its base, meaning there are two digits, 0 and 1.

The following table shows how computers store the decimal number Two of the improvements seen in C 7. You can insert underscores anywhere into the digits of a number literal, including decimal, binary, or hexadecimal notation, to improve legibility.

To use binary notation, that is, Base 2, using only 1s and 0s, start the number literal with 0b. To use hexadecimal notation, that is, Base 16, using 0 to 9 and A to F, start the number literal with 0x. Let's enter some code to see some examples. Run the console app and note the result is that all three numbers are the same, as shown in the following output: True True Computers can always exactly represent integers using the int type or one of its sibling types such as long and short.

The float and double types store real numbers using single- and double-precision floating points. As you can see, the number However, some numbers can't, something that we'll be exploring shortly. Writing code to explore number sizes C has an operator named sizeof that returns the number of bytes that a type uses in memory.

Some types have members named MinValue and MaxValue, which return the minimum and maximum values that can be stored in a variable of that type. We are now going to use these features to create a console application to explore number types. Inside the Main method, type statements to show the size of three number data types, as shown in the following code: Console. You must type them on a single line, or you will get compile errors.

Run the console application by entering dotnet run, and view the output, as shown in the following screenshot: Figure 2. A double variable uses eight bytes of memory and can store much bigger values! A decimal variable uses 16 bytes of memory and can store big numbers, but not as big as a double type.

But you may be asking yourself, why might a double variable be able to store bigger numbers than a decimal variable, yet it's only using half the space in memory? Well, let's now find out! Comparing double and decimal types You will now write some code to compare double and decimal values. Although it isn't hard to follow, don't worry about understanding the syntax right now: 1.

Under the previous statements, enter statements to declare two double variables, add them together and compare them to the expected result, and write the result to the console, as shown in the following code: Console.

Run the console application and view the result, as shown in the following output: Using doubles: 0. More Information: You can read more about why 0. An example of this may be when you're measuring a person's height. The problem with the preceding code is illustrated by how the computer stores the number 0. To represent 0. The number 0. During the First Gulf War, an American Patriot missile battery used double values in its calculations. Copy and paste the statements that you wrote before that used the double variables.

Modify the statements to use decimal and rename the variables to c and d, as shown in the following code: Console. Run the console application and view the result, as shown in the following output: Using decimals: 0. For example, 0. Good Practice: Use int for whole numbers and double for real numbers that will not be compared to other values. Use decimal for money, CAD drawings, general engineering, and wherever the accuracy of a real number is important.

The double type has some useful special values: double. NaN means not-a-number, double. Epsilon is the smallest positive number that can be stored in a double, and double. Infinity means an infinitely large value. You don't need to fully understand them yet, as they are covered more in Chapter 3, Controlling Flow and Converting Types. Using Visual Studio Code workspaces Before we create any more projects, let's talk about workspaces.

Although we could continue to create and open separate folders for each project, it can be useful to have multiple folders open at the same time. Visual Studio has a feature called workspaces that enables this. Let's create a workspace for the two projects we have created so far in this chapter: 1. Enter Chapter02 for the workspace name, change to the Chapter02 folder, and click Save, as shown in the following screenshot: [ 51 ] Speaking C Figure 2. Navigate to File Add Folder to Workspace… 4.

Select the Basics folder, click Add, and note that both Basics and Numbers are now part of the Chapter02 workspace. Good Practice: When using workspaces, be careful when entering commands in Terminal. Be sure that you are in the correct folder before entering potentially destructive commands! You will see how in the next task. Storing any type of object There is a special type named object that can store any type of data, but its flexibility comes at the cost of messier code and possibly poor performance.

Because of those two reasons, you should avoid it whenever possible. The following steps show how to use object types if you need to use them: 1. Create a new folder named Variables and add it to the Chapter02 workspace. Navigate to Terminal New Terminal. Select the Variables project, as shown in the following screenshot: Figure 2. Enter the command to create a new console application: dotnet new console. Navigate to View Command Palette. Enter and select OmniSharp: Select Project.

Select the Variables project, and if prompted, click Yes to add required assets to debug. In TERMINAL, execute the code by entering dotnet run, and note that the fourth statement cannot compile because the data type of the name variable is not known by the compiler.

Add comment double slashes to the beginning of the statement that cannot compile to "comment it out. In TERMINAL, execute the code by entering dotnet run, and note that the compiler can access the length of a string if the programmer explicitly tells the compiler that the object variable contains a string, as shown in the following output: Amir is 1.

Amir has 4 characters. The object type has been available since the first version of C , but C 2. Storing dynamic types There is another special type named dynamic that can also store any type of data, but even more than object, its flexibility comes at the cost of performance. The dynamic keyword was introduced in C 4. However, unlike object, the value stored in the variable can have its members invoked without an explicit cast. Let's make use of a dynamic type: 1.

This is because the compiler cannot check what the type is during build time. Instead, the CLR checks for the member at runtime and throws an exception if it is missing. You will learn more about them and how to handle them in Chapter 3, Controlling Flow and Converting Types. Declaring local variables Local variables are declared inside methods, and they only exist during the execution of that method, and once the method returns, the memory allocated to any local variables is released.

Strictly speaking, value types are released while reference types must wait for a garbage collection. You will learn about the difference between value types and reference types in Chapter 6, Implementing Interfaces and Inheriting Classes. Specifying and inferring the type of a local variable Let's explore local variables declared with specific types and using type inference. You can use the var keyword to declare local variables.

A literal number without a decimal point is inferred as an int variable, that is, unless you add the L suffix, in which case, it infers a long variable. A literal number with a decimal point is inferred as double unless you add the M suffix, in which case, it infers a decimal variable, or the F suffix, in which case, it infers a float variable.

Double quotes indicate a string variable, single quotes indicate a char variable, and the true and false values infer a bool type. Personally, I use it only when the type is obvious. For example, in the following code statements, the first statement is just as clear as the second in stating what the type of the xml variable is, but it is shorter.

However, the third statement isn't clear, so the fourth is better. If in doubt, spell it out! At the top of the class file, import some namespaces, as shown in the following code: using System. IO; using System. Xml; 4. You can determine the default value of a type using the default operator. The string type is a reference type.

This means that string variables contain the memory address of a value, not the value itself. A reference type variable can have a null value, which is a literal that indicates that the variable does not reference anything yet. You'll learn more about value types and reference types in Chapter 6, Implementing Interfaces and Inheriting Classes.

In the Main method, add statements to show the default values of an int, bool, DateTime, and string, as shown in the following code: Console. For example, you may do this when you need to store four names in a string array. The code that you will write next will allocate memory for an array for storing four string values. It will then store string values at index positions 0 to 3 arrays count from zero, so the last item is one less than the length of the array.

Finally, it will loop through each item in the array using a for statement, something that we will cover in more detail in Chapter 3, Controlling Flow and Converting Types. Let's look at how to use an array in detail: 1. In the Chapter02 folder, create a new folder named Arrays. Add the Arrays folder to the Chapter02 workspace. Create a new Terminal window for the Arrays project.

Create a new console application project in the Arrays folder. Select Arrays as the current project for OmniSharp. In the Arrays project, in Program. Run the console app and note the result, as shown in the following output: Kate Jack Rebecca Tom Arrays are always of a fixed size at the time of memory allocation, so you need to decide how many items you want to store before instantiating them. Arrays are useful for temporarily storing multiple items, but collections are a more flexible option when adding and removing items dynamically.

You don't need to worry about collections right now, as we will cover them in Chapter 8, Working with Common. NET Types. Working with null values You have now seen how to store primitive values like numbers in variables. But what if a variable does not yet have a value? How can we indicate that? C has the concept of a null value, which can be used to indicate that a variable has not been set.

Making a value type nullable By default, value types like int and DateTime must always have a value, hence their name. Sometimes, for example, when reading values stored in a database that allows empty, missing, or null values, it is convenient to allow a value type to be null. We call this a nullable value type. You can enable this by adding a question mark as a suffix to the type when declaring a variable.

Let's see an example: 1. In the Chapter02 folder, create a new folder named NullHandling. Add the NullHandling folder to the Chapter02 workspace. Create a new Terminal window for the NullHandling project. Create a new console application project in the NullHandling folder. Select NullHandling as the current project for OmniSharp. In the NullHandling project, in Program. WriteLine thisCouldBeNull. GetValueOrDefault ; 7. Comment out the statement that gives a compile error. Run the application and view the result, as shown in the following output: 0 7 7 The first line is blank because it is outputting the null value!

Understanding nullable reference types The use of the null value is so common, in so many languages, that many experienced programmers never question the need for its existence. But there are many scenarios where we could write better, simpler code if a variable is not allowed to have a null value. Since this is a big change for C , Microsoft decided to make the feature opt-in.

Even Microsoft has not had time to fully implement this new feature in all the main. NET 5 packages. Non-nullable reference types are not supported. This is the approach Microsoft is using internally while it updates its own packages to use this new feature. Enabling nullable and non-nullable reference types To enable the feature at the project level, add the following to your project file: enable To disable the feature at the file level, add the following to the top of a code file: nullable disable To enable the feature at the file level, add the following to the top of a code file: nullable enable Declaring non-nullable variables and parameters If you enable nullable reference types and you want a reference type to be assigned the null value, then you will have to use the same syntax as making a value type nullable, that is, adding a?

So, how do nullable reference types work? Let's look at an example. When storing information about an address, you might want to force a value for the street, city, and region, but the building can be left blank, that is, null: 1. In NullHandling. After a few seconds, note that the C extension warns of problems with non-nullable fields like Street, as shown in the following screenshot: Figure 2.

Empty; 6. Note the warnings, as shown in the following screenshot: Figure 2. Starting with C 8. You do this using the null-coalescing operator,?? Console applications are text-based and are run at the command line. They typically perform simple tasks that need to be scripted, such as compiling a file or encrypting a section of a configuration file. Equally, they can also have arguments passed to them to control their behavior. An example of this would be to create a new console app using the F language with a specified name instead of using the name of the current folder, as shown in the following command line: dotnet new console -lang "F " --name "ExploringConsole" Displaying output to the user The two most common tasks that a console application performs are writing and reading data.

We have already been using the WriteLine method to output, but if we didn't want a carriage return at the end of the lines, we could have used the Write method. Formatting using numbered positional arguments One way of generating formatted strings is to use numbered positional arguments. This feature is supported by methods like Write and WriteLine, and for methods that do not support the feature, the string parameter can be formatted using the Format method of string.

Add a new console application project named Formatting to the Chapter02 folder and workspace. Formatting using interpolated strings C 6. In the Main method, enter a statement at the bottom of the Main method, as shown in the following code: Console. But for code examples in a book, where lines need to wrap over multiple lines, this can be tricky. For many of the code examples in this book, I will use numbered positional arguments. Understanding format strings A variable or expression can be formatted using a format string after a comma or colon.

The currency format will be determined by the current thread. For instance, if you run this code on a PC in the UK, you'll get pounds sterling with commas as the thousand separators, but if you run this code on a PC in Germany, you will get Euros with dots as the thousand separators. Alignment values are integers. Positive integers are right-aligned and negative integers are left-aligned. For example, to output a table of fruit and how many of each there are, we might want to left-align the names within a column of 8 characters and right-align the counts formatted as numbers with zero decimal places within a column of six characters: 1.

Run the console app and note the effect of the alignment and number format, as shown in the following output: Name Count Apples 1, Bananas 56, [ 64 ] Chapter 02 More Information: You can read more details about formatting types in. This method waits for the user to type some text, then as soon as the user presses Enter, whatever the user has typed is returned as a string value: 1. In the Main method, type statements to ask the user for their name and age and then output what they entered, as shown in the following code: Console.

ReadLine ; Console. Run the console application. Importing a namespace You might have noticed that unlike our very first application in Chapter 1, Hello, C! This is because System is a namespace, which is like an address for a type. To refer to someone exactly, you might use Oxford. The System. WriteLine line tells the compiler to look for a method named WriteLine in a type named Console in a namespace named System.

To simplify our code, the dotnet new console command added a statement at the top of the code file to tell the compiler to always look in the System namespace for types that haven't been prefixed with their namespace, as shown in the following code: using System; [ 65 ] Speaking C We call this importing the namespace. The effect of importing a namespace is that all available types in that namespace will be available to your program without needing to enter the namespace prefix and will be seen in IntelliSense while you write code.

Simplifying the usage of the console In C 6. Then, we won't need to enter the Console type throughout our code. We can use Visual Studio Code's Replace feature to remove the times we have previously written Console. Add a statement to statically import the System. Console class to the top of the Program. Console; 2. Select the first Console. Navigate to Edit Replace and note that an overlay dialog appears ready for you to enter what you would like to replace Console.

Getting key input from the user We can get key input from the user using the ReadKey method. This method waits for the user to press a key or key combination that is then returned as a ConsoleKeyInfo value: 1. Key, arg1: key. KeyChar, arg2: key. Modifiers ; 2. Run the console application, press the K key, and note the result, as shown in the following output: Press any key combination: k Key: K, Char: k, Modifiers: 0 3.

Run the console application, hold down Shift and press the K key, and note the result, as shown in the following output: Press any key combination: K Key: K, Char: K, Modifiers: Shift 4. Run the console application, press the F12 key, and note the result, as shown in the following output: Press any key combination: Key: F12, Char: , Modifiers: 0 When running a console application in Terminal within Visual Studio Code, some keyboard combinations will be captured by the code editor or operating system before they can be processed by your app.

Getting arguments You might have been wondering what the string[] args arguments are in the Main method. They're an array used to pass arguments into a console application; let's take a look to see how it works. Command-line arguments are separated by spaces. Other characters like hyphens and colons are treated as part of an argument value. To include spaces in an argument value, enclose the argument value in single or double quotes.

Imagine that we want to be able to enter the names of some colors for the foreground and background, and the dimensions of the Terminal window at the command line. We would be able to read the colors and numbers by reading them from the args array, which is always passed into the Main method of a console application. Create a new folder for a console application project named Arguments and add it to the Chapter02 workspace. Console type and a statement to output the number of arguments passed to the application, as shown highlighted in the following code: using System; using static System.

Console type in all future projects to simplify your code, as these instructions will not be repeated every time. Run the console application and view the result, as shown in the following output: There are 0 arguments. In TERMINAL, enter some arguments after the dotnet run command, as shown in the following command line: dotnet run firstarg second-arg third:arg "fourth arg" 5.

Note the result indicates four arguments, as shown in the following output: There are 4 arguments. In TERMINAL, repeat the same arguments after the dotnet run command, as shown in the following command line: dotnet run firstarg second-arg third:arg "fourth arg" 8. Note the result shows the details of the four arguments, as shown in the following output: There are 4 arguments. The cursor size can be an integer value from 1, meaning a line at the bottom of the cursor cell, up to , meaning a percentage of the height of the cursor cell.

The System namespace is already imported so that the compiler knows about the ConsoleColor and Enum types. If you cannot see either of these types in the IntelliSense list, it is because you are missing the using System; statement at the top of the file. Add statements to warn the user if they do not enter three arguments and then parse those arguments and use them to set the color and dimensions of the console window, as shown in the following code: if args.

Length 2. On Windows, this will run, but the cursor will not change size. On macOS, you'll see an unhandled exception, as shown in the following screenshot: [ 69 ] Speaking C Figure 2. Although a console application running on Linux can change its cursor size, on macOS, it cannot, and complains if you try. Handling platforms that do not support an API So how do we solve this problem?

We can solve this by using an exception handler. You will learn more details about the try-catch statement in Chapter 3, Controlling Flow and Converting Types, so for now, just enter the code. Rerun the console application; note the exception is caught, and a friendlier message is shown to the user. Another way to handle differences in operating systems is to use the OperatingSystem class, as shown in the following code: if OperatingSystem. Practicing and exploring Test your knowledge and understanding by answering some questions, get some hands-on practice, and explore the topics covered in this chapter with deeper research.

Exercise 2. I want you to "think outside the book" so I have deliberately not provided all the answers in the book. I want to encourage you to get in the good habit of looking for help elsewhere, following the principle of "teach a person to fish.

A person's telephone number 2. A person's height 3. A person's age 4. A person's salary 5. A book's ISBN 6. A book's price 7. A book's shipping weight 8. A country's population 9. The number of stars in the universe The number of employees in each of the small or medium businesses in the United Kingdom up to about 50, employees per business Exercise 2.

In the next chapter, you will learn about operators, branching, looping, and converting between types. They usually return a new value that is the result of the operation that can be assigned to a variable. Let us write some example code to show how they work: 1. If you have completed the previous chapters, then you will already have a Code folder in your user folder. If not, create it. In the Code folder, create a folder named Chapter Start Visual Studio Code and close any open workspace or folder.

Save the current workspace in the Chapter03 folder as Chapter Create a new folder named Operators and add it to the Chapter03 workspace. Open Program. Statically import System. Before running the console application, ask yourself a question: what do you think the value of b will be when output?

If you need to increment before the assignment, then use the prefix operator. Rerun the console application and note the result, as shown in the following output: a is 4, b is 3 c is 4, d is 4 Good Practice: Due to the confusion between prefix and postfix for the increment and decrement operators when combined with assignment, the Swift programming language designers decided to drop support for this operator in version 3. Perform the operations as separate statements.

Binary arithmetic operators Increment and decrement are unary arithmetic operators. Other arithmetic operators are usually binary and allow you to perform arithmetic operations on two numbers as the following shows: 1.

Imagine you have eleven sweets and three friends. How can you divide the sweets between your friends? You can give three sweets to each of your friends, and there will be two left over. Those two sweets are the modulus, also known as the remainder after dividing. If you have twelve sweets, then each friend gets four of them, and there are none left over, so the remainder would be 0. Rerun the console application and note the result, as shown in the following output: g is Let's explore binary logical operators that operate on two Boolean values: [ 76 ] Chapter 03 1.

Create a new folder and console application named BooleanOperators and add it to the Chapter03 workspace. Remember to use the Command Palette to select BooleanOperators as the active project. Good Practice: Remember to statically import the System. Console type to simplify statements in a console app. For the OR logical operator, either operand can be true for the result to be true. In Chapter 4, Writing, Debugging, and Testing Functions, you will learn about functions in more detail, but I need to introduce functions now to explain conditional logical operators, also known as short-circuiting Boolean operators.

A function executes statements and then returns a value. That value could be a Boolean value like true that is used in a Boolean operation. Let's make use of conditional logical operators: 1. True stuff. False 4. Run the console app, view the result, and note that the function does run when combined with the a variable. It does not run when combined with the b variable because the b variable is false so the result will be false anyway, so it does not need to execute the function, as shown in the following output: I am doing some stuff.

Good Practice: Now you can see why the conditional logical operators are described as being short-circuiting. They can make your apps more efficient, but they can also introduce subtle bugs in cases where you assume that the function would always be called. It is safest to avoid them when used in combination with functions that cause side effects. Binary shift operators can perform some common arithmetic calculations much faster than traditional operators.

Let's explore bitwise and binary shift operators: 1. Create a new folder and console application named BitwiseAndShiftOperators and add it to the workspace. This is the equivalent of multiplying by 8 but CPUs can perform a bit-shift faster. The 3 result is because the 1-bits in b were shifted one column into the 2- and 1-bit columns. The two selection statements in C are if and switch. You can use if for all your code, but switch can simplify your code in some common scenarios such as when there is a single variable that can have multiple values that each require different processing.

Branching with the if statement The if statement determines which branch to follow by evaluating a Boolean expression. If the expression is true, then the block executes. The else block is optional, and it executes if the if expression is false. The if statement can be nested. Create a folder and console application named SelectionStatements and add it to the workspace. Add the following statements inside the Main method to check whether this console application has any arguments passed to it: if args.

Run the console application by entering the following command into the TERMINAL: dotnet run Why you should always use braces with if statements As there is only a single statement inside each block, the preceding code could be written without the curly braces, as shown in the following code: if args. For 18 months after Apple's iOS 6 was released, in September , it had a bug in its Secure Sockets Layer SSL encryption code, which meant that any user running Safari, the device's web browser, who tried to connect to secure websites, such as their bank, was not properly secure because an important check was being accidentally skipped.

Your code is not "more efficient" without them; instead, it is less maintainable and potentially more dangerous. The if statement can use the is keyword in combination with declaring a local variable to make your code safer: 1.

Add statements to the end of the Main method so that if the value stored in the variable named o is an int, then the value is assigned to the local variable named i, which can then be used inside the if statement. Run the console application and view the results, as shown in the following output: o is not an int so it cannot multiply! Delete the double-quote characters around the "3" value so that the value stored in the variable named o is an int type instead of a string type.

Every case statement is related to the single expression. Enter some statements for a switch statement after the if statements that you wrote previously. You should note that the first line is a label that can be jumped to, and the second line generates a random number.

The goto keyword is frowned upon by most programmers but can be a good solution to code logic in some scenarios. However, you should use it sparingly. Run the console application multiple times in order to see what happens in various cases of random numbers, as shown in the following example output: bash The case values no longer need to be literal values; they can be patterns.

Let's see an example of pattern matching with the switch statement using a folder path. If you are using macOS, then swap the commented statement that sets the path variable and replace my username with your user folder name: 1.

IO; 2. Open Path. Combine path, "file. OpenOrCreate, FileAccess. Run the console app and note that the variable named s is declared as a Stream type so it could be any subtype of stream, like a memory stream or file stream.

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Read this complete and Schema. Its new Auto I can tell can stop those sites from loading possibly false positives. Most enterprises struggle affordable plans for. Have Windows, iOS, these passwords.

In Solution Explorer we can copy the AppProperties. The copied file can then be renamed based on the platform. For example see image below the Windows specific code would be in a file called AppProperties. For example, the AppProperties. We also needed to add the partial keyword to the class definition.

After adding files for each platform, if you attempt to build the Core project it will fail with an error indicating that there are multiple definitions of the PlatformName constant. What we need to do is to only include one platform specific file at a time. Currently the Core project is configured with a single TargetFramework, netstandard2.

This means that the only API that can be accessed are those defined by netstandard2. If we want to include platform specific code, or want to access platform specific APIs, we need to change the project to target multiple frameworks. We also need to create a file called global.

Extra nuget package:. For example, when we build the Core library, we see that four DLLs are built — effectively increasing the built time by four times!!! The new project format includes all files nested in the project folder by default. Then we can specifically include files for each platform that is built. The project file now looks like this:.

This technique for including platform specific code in a common library is used by popular frameworks such as ReactiveUI and MvvmCross , as well as Microsoft libraries such as Xamarin Essentials. Source code. Hi Nick, Thanks for this very nice post! Part 1 — Understanding the Xamarin Mobile Platform. Part 4 — Dealing with Multiple Platforms.

Part 5 — Practical Code Sharing Strategies. Part 6 - Testing and App Store Approvals. The principles outlined in this document are put into practice in the sample application Tasky , as well as pre-built applications like Xamarin CRM. It demonstrates the basics of creating a cross-platform application with Xamarin and uses a local SQLite database.

It covers a layered architecture that structures code for re-use across multiple platforms, and describes different software patterns that can be used within that architecture. Examples are given of common application functions like file and network operations and how they can be built in a cross-platform way. Finally, it briefly discusses testing, and provides references to a case study that puts these principles into action.

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