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* First draft of new tutorial Learn the structure of a C# program, and explore the string class. proofread and tighten language. respond to feedback 2nd draft Move more code earlier. Tighten vocabulary discussions. Update outline start on the next draft. add section on searching strings fix build errors finish the string tutorial. reorder: ready for proofread. proofread update to use new syntax Update Tutorial to use the new engine typo in the title * build test, try samples * 2nd draft of the numbers tutorial. * proofread the second tutorial and create the third Branching and looping is ready for initial review. * respond to feedback on first tutorial. * proof read 3rd tutorial And add links to other C# Guide content * Remove links to upcoming tutorials. * Respond to feedback. * fix yaml parsing error. * More feedback. * feedback from team review Configure ms.technology for all quick starts to be devlang-csharp-interactive. Update .NET home page and C# Guide home page to point to the interactive tutorials. * Describe booleans, and update metadata. * add a tip about compiler messages * update timings of tutorials, update tip text * final review.
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,257 @@ | ||
| ### YamlMime:YamlDocument | ||
| documentType: Tutorial | ||
| title: Branches and loops | ||
| metadata: | ||
| title: Branches and loops | ||
| description: In this tutorial about branches and loops, you'll use your browser to learn C# interactively. You're going to write C# code and see the results of compiling and running your code directly in the browser. | ||
| audience: Developer | ||
| level: Beginner | ||
| displayType: two-column | ||
| interactive: csharp | ||
| items: | ||
| - durationInMinutes: 1 | ||
| content: | | ||
| This tutorial teaches you about how to write code that examines variables and changes execution path based on those variables. You'll write C# interactively, using your browser to write C# and see the results of compiling and running your code. It contains a series of lessons that explore branching and looping constructs in C#. These lessons teach you the fundamentals of the C# language. | ||
| - title: Make decisions using the if statement | ||
| durationInMinutes: 4 | ||
| content: | | ||
| Run the following code in the interactive window. To do that, type the following code block in the interactive window and click the **Run** button: | ||
| ```csharp | ||
| int a = 5; | ||
| int b = 6; | ||
| if (a + b > 10) | ||
| Console.WriteLine("The answer is greater than 10."); | ||
| ``` | ||
| Modify the declaration of `b` so that the sum is less than 10: | ||
| ```csharp | ||
| int b = 3; | ||
| ``` | ||
| Click the **Run** button again. Because the answer is less than 10, nothing is printed. The **condition** you're testing is false. You don't have any code to execute because you've only | ||
| written one of the possible branches for an `if` statement: the true branch. | ||
| > [!TIP] | ||
| > As you explore C# (or any programming language), you'll | ||
| > make mistakes when you write code. The **compiler** will | ||
| > find those errors and report them to you. When the output | ||
| > contains error messages, look closely at the example code, | ||
| > and the code in the interactive window to see what to fix. | ||
| > That exercise will help you learn the structure of C# code. | ||
| This first sample shows the power of `if` and boolean types. A *boolean* is a variable that can have one of two values: `true` or `false`. C# defines a special type, `bool` for boolean variables. The `if` statement checks the value of a `bool`. When the value is `true`, the statement following the `if` executes. Otherwise, it is skipped. | ||
| This process of checking conditions and executing statements based on those conditions is very powerful. Let's explore more. | ||
| - title: Make if and else work together | ||
| durationInMinutes: 10 | ||
| content: | | ||
| To execute different code in both the true and false branches, you | ||
| create an `else` branch that executes when the condition is false. Try this: | ||
| ```csharp | ||
| int a = 5; | ||
| int b = 3; | ||
| if (a + b > 10) | ||
| Console.WriteLine("The answer is greater than 10"); | ||
| else | ||
| Console.WriteLine("The answer is not greater than 10"); | ||
| ``` | ||
| The statement following the `else` keyword executes only when the condition being tested is `false`. Combining `if` and `else` with boolean conditions provides all the power you need. | ||
| > [!IMPORTANT] | ||
| > The indentation under the `if` and `else` statements is for human readers. | ||
| > The C# language doesn't treat indentation or whitespace as significant. | ||
| > The statement following the `if` or `else` keyword will be executed based | ||
| > on the condition. All the samples in this tutorial follow a common | ||
| > practice to indent lines based on execution. | ||
| Because indentation is not significant, you need to use `{` and `}` to | ||
| indicate when you want more than one statement to be part of the block | ||
| that executes conditionally. C# programmers typically use those braces | ||
| on all `if` and `else` clauses. The following example is the same as what you | ||
| just created. Try it. | ||
| ```csharp | ||
| int a = 5; | ||
| int b = 3; | ||
| if (a + b > 10) | ||
| { | ||
| Console.WriteLine("The answer is greater than 10"); | ||
| } | ||
| else | ||
| { | ||
| Console.WriteLine("The answer is not greater than 10"); | ||
| } | ||
| ``` | ||
| > [!TIP] | ||
| > Through the rest of this tutorial, the code samples all include the braces, | ||
| > following accepted practices. | ||
| You can test more complicated conditions: | ||
| ```csharp | ||
| int a = 5; | ||
| int b = 3; | ||
| int c = 4; | ||
| if ((a + b + c > 10) && (a > b)) | ||
| { | ||
| Console.WriteLine("The answer is greater than 10"); | ||
| Console.WriteLine("And the first number is greater than the second"); | ||
| } | ||
| else | ||
| { | ||
| Console.WriteLine("The answer is not greater than 10"); | ||
| Console.WriteLine("Or the first number is not greater than the second"); | ||
| } | ||
| ``` | ||
| The `&&` represents "and". It means both conditions must be true to execute | ||
| the statement in the true branch. These examples also show that you can have multiple | ||
| statements in each conditional branch, provided you enclose them in `{` and `}`. | ||
| You can also use `||` to represent "or": | ||
| ```csharp | ||
| int a = 5; | ||
| int b = 3; | ||
| int c = 4; | ||
| if ((a + b + c > 10) || (a > b)) | ||
| { | ||
| Console.WriteLine("The answer is greater than 10"); | ||
| Console.WriteLine("Or the first number is greater than the second"); | ||
| } | ||
| else | ||
| { | ||
| Console.WriteLine("The answer is not greater than 10"); | ||
| Console.WriteLine("And the first number is not greater than the second"); | ||
| } | ||
| ``` | ||
| - title: Use loops to repeat operations | ||
| durationInMinutes: 6 | ||
| content: | | ||
| Another important concept to create larger programs is **loops**. You'll | ||
| use loops to repeat statements that you want executed more than once. Try | ||
| this code in the interactive window: | ||
| ```csharp | ||
| int counter = 0; | ||
| while (counter < 10) | ||
| { | ||
| Console.WriteLine("Hello World! The counter is " + counter); | ||
| counter++; | ||
| } | ||
| ``` | ||
| The `while` statement checks a condition and executes the statement | ||
| following the `while`. It will repeat checking the condition and | ||
| executing those statements until the condition is false. | ||
| There's one other new operator in this example. The `++` after | ||
| the `counter` variable is the **increment** operator. It adds 1 | ||
| to the value of counter, and stores that value in the counter variable. | ||
| > [!IMPORTANT] | ||
| > Make sure that the `while` loop condition does switch to | ||
| > false as you execute the code. Otherwise, you create an | ||
| > **infinite loop** where your program never ends. Let's | ||
| > not demonstrate that, because the engine that runs your | ||
| > code will time out and you'll see no output from your program. | ||
| The `while` loop tests the condition before executing the code | ||
| following the `while`. The `do` ... `while` loop executes the | ||
| code first, and then checks the condition. It looks like this: | ||
| ```csharp | ||
| int counter = 0; | ||
| do | ||
| { | ||
| Console.WriteLine("Hello World! The counter is " + counter); | ||
| counter++; | ||
| } while (counter < 10); | ||
| ``` | ||
| This `do` loop and the earlier `while` loop work the same. | ||
| Let's move on to one last loop statement. | ||
| - title: Work with the for loop | ||
| durationInMinutes: 5 | ||
| content: | | ||
| Another common loop statement that you'll see in C# code is the | ||
| `for` loop. Try this code in the interactive window: | ||
| ```csharp | ||
| for(int counter = 0; counter < 10; counter++) | ||
| { | ||
| Console.WriteLine("Hello World! The counter is " + counter); | ||
| } | ||
| ``` | ||
| This does the same work as the `while` loop and the `do` loop you've | ||
| already used. The `for` statement has three parts that control | ||
| how it works. | ||
| The first part is the **for initializer**: `for counter = 0;` declares | ||
| that `counter` is the loop variable, and sets its initial value to `0`. | ||
| The middle part is the **for condition**: `counter < 10` declares that this | ||
| `for` loop continues to execute as long as the value of counter is less than 10. | ||
| The final part is the **for iterator**: `counter++` specifies how to modify the loop | ||
| variable after executing the block following the `for` statement. Here, it specifies | ||
| that `counter` should be incremented by 1 each time the block executes. | ||
| Experiment with these yourself. Try each of the following: | ||
| - Change the initializer to start at a different value. | ||
| - Change the condition to stop at a different value. | ||
| When you're done, let's move on to write some code yourself to | ||
| use what you've learned. | ||
| - title: Combining branches and loops | ||
| durationInMinutes: 12 | ||
| content: | | ||
| Now that you've seen the `if` statement and the looping | ||
| constructs in the C# language, see if you can write C# code to | ||
| find the sum of all integers 1 through 20 that are divisible | ||
| by 3. Here are a few hints: | ||
| - The `%` operator gives you the remainder of a division operation. | ||
| - The `if` statement givesx you the condition to see if a number should be part of the sum. | ||
| - The `for` loop can help you repeat a series of steps for all the numbers 1 through 20. | ||
| Try it yourself. Then check how you did. | ||
| - title: Complete challenge | ||
| durationInMinutes: 1 | ||
| content: | | ||
| Did you come up with something like this? | ||
| ```csharp | ||
| int sum = 0; | ||
| for (int number = 1; number < 21; number++) | ||
| { | ||
| if (number % 3 == 0) | ||
| { | ||
| sum = sum + number; | ||
| } | ||
| } | ||
| Console.WriteLine("The sum is " + sum); | ||
| ``` | ||
| content: | | ||
| You've completed the "branches and loops" tutorial. You can learn more about these concepts in these topics: | ||
| [If and else statement](../language-reference/keywords/if-else.md) | ||
| [While statement](../language-reference/keywords/while.md) | ||
| [Do statement](../language-reference/keywords/do.md) | ||
| [For statement](../language-reference/keywords/for.md) | ||
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