Variables in C#

Programmes work by manipulating data stored in memory. These storage areas come under the general heading of Variables. In this section, you'll see how to set up and use variables. You'll see how to set up both text and number variables. By the end of this section, you'll have written a simple calculator programme. We'll start with something called a String variable.

String Variables in C#.NET

The first type of variable we'll take a look at is called a String. String variables are always text. We'll write a little programme that takes text from a text box, store the text in a variable, and then display the text in a message box.

But bear in mind that a variable is just a storage area for holding things that you'll need later. Think of them like boxes in a room. The boxes are empty until you put something in them. You can also place a sticker on the box, so that you'll know what's in it. Let's look at a programming example.

If you've got your project open from the previous section, click File from the menu bar at the top of Visual C#. From the File menu, click Close Solution. Start a new project by clicking File again, thenNew Project. From the New Project dialogue box, click on Windows Application. For the Name, typeString Variables.

Click OK, and you'll see a new form appear. Add a button to the form, just like you did in the previous section. Click on the button to select it (it will have the white squares around it), and then look for the Properties Window in the bottom right of Visual Studio. Set the following Properties for your new button:

Name: btnStrings
Location: 90, 175
Size: 120, 30
Text: Get Text Box Data

Your form should then look like this:

We can add two more controls to the form, a Label and a Text Box. When the button is clicked, we'll get the text from the text box and display whatever was entered in a message box.

A Label is just that: a means of letting your users know what something is, or what it is for. To add a Label to the form, move your mouse over to the Toolbox on the left. Click the Label item underCommon Controls:

Now click once on your form. A new label will be added:

The Label has the default text of label1. When your label is selected, it will have just the one white square in the top left. When it is selected, the Properties Window will have changed. Notice that the properties for a label are very similar to the properties for a button - most of them are the same!

Change the following properties of your label, just like you did for the button:

Location: 10, 50
Text: Name

You don't really need to set a size, because Visual C# will automatically resize your label to fit your text. But your Form should look like this:

Move your mouse back over to the Toolbox. Click on the TextBox entry. Then click on your form. A new Text Box will be added, as in the following image:

Instead of setting a location for your text box, simply click it with your left mouse button. Hold your left mouse button down, and the drag it just to the right of the Label.

Notice that when you drag your text box around, lines appear on the form. These are so that you can align your text box with other controls on the form. In the image below, we've aligned the text box with the left edge of the button and the top of the Label.

OK, time to add some code. Before you do, click File > Save All from the menu bar at the top of Visual C#. You can also run your programme to see what it looks like. Type some text in your text box, just to see if it works. Nothing will happen when you click your button, because we haven't written any code yet. Let's do that now. Click the red X on your form to halt the programme, and you'll be returned to Visual C#.

Adding C# Code to a Button and message box

What we want to do now is to display a message box whenever the button is clicked. So we need the coding window. To see the code for the button, double click the button you added to the Form. When you do, the coding window will open, and your cursor will be flashing inside of the button code. It will look like this:

The only difference from the last time you saw this screen is the addition of the code for the button. This code:

private void button1_Click(object sender, EventArgs e)
{

}

This is just another Method, a piece of code that does something. The name of the Method isbutton1_Click. It's called button1 because that's currently the Name of the button. When you changed the Text, Location, and Size properties of the button, you could have also changed the Name property from button1 (the default Name) to something else.

The _Click part after button1 is called an Event. Other events are MouseDown, LocationChanged, TextChanged, and lots more. You'll learn more about Events later.

After _Click, and in between a pair of round brackets, we have this:

object sender, EventArgs e

These two are know as arguments. One arguments is called sender, and the other is called e. Again, you'll learn more about arguments later, so don't worry about them for now.

Notice that there is a pair of curly brackets for the button code:

private void button1_Click(object sender, EventArgs e)
{

}

We want to display a message box, with some text on it. This is quite easy to do in C#.
Position your cursor between the two curly brackets. Then type a capital letter "M". You'll see the IntelliSense list appear:

Now type "ess" after the "M". IntelliSense will jump down:

The only options that start with Mess are all Message ones. The one we want is MessageBox. You can either just type the rest, or even easier is to press the down arrow on your keyboard to move down to MessageBox:

When you have MessageBox selected, hit the enter key on your keyboard (or double click the entry on the list). The code will be added for you:

Now type a full stop (period) after the "x" of MessageBox. The IntelliSense list will appear again:

There are only three items on the list now, and all Methods (you can tell they are Methods because they have the purple block icon next to them) Double click on Show, and it will be added to your C# code:

Because Show is a Method, we need some round brackets. The text for our message box will go between the round brackets. So type a left round bracket, just after the "w" of "Show":

As soon as you type the left round bracket after the "w", you'll see all the different ways that the Show method can be used. There are 21 different ways in total. Fortunately, you don't have to hunt through them all! Type the following, after the left round bracket (Don't forget the double quotation marks.):

"My First Message"

After the final double quote mark, type a right round bracket. Then finish off the line by typing a semi-colon ( ; ), Your coding window will then look like this:

The text in the dark reddish colour is what will be displayed in your message box. To try it out, save your work by clicking File from the menu bar at the top of Visual Studio. From the File menu, clickSave All. You'll then see the same Save box you saw for the Console Application. Save the project.
Run your programme by clicking Debug > Start Debugging. Or just press the F5 key on your keyboard. Your programme will look like this:

Click your button to see your Message Box:

Congratulations! It's your first message! In the next part, we'll explore other things you can do with a message box.

Adding Controls to a Blank C# Form

The first thing we'll do is to add a button to the blank form. We'll then write a single line of code, so that you can see how things work.

If you want to add a control to a form, you can use the Toolbox on the left of Visual Studio. Move your mouse over to the Toolbox, and click the plus symbol next to Common Controls. You should see the following list of things that you can add to your form:

Click the Button item under the Common Controls heading. This will select it. Now click once anywhere on your form. A button will be drawn for you, and your Form will look like this:

(You can also hold down your left mouse button and drag out a button to the size you want it.)

A button is something you want people to click on. When they do, the code you write gets executed. The text on the button, which defaults to "button1", can be changed. You can add anything you like here, but it should be something that's going to be useful for your users, such as "Open a text file", or "Calculate Now".

Your First C# Windows Form

From now on, we're going to be creating Windows Applications, rather than Console Applications. Windows Applications make use of something called a Form. The Form is blank at first. You then add control to your form, things like buttons, text boxes, menus, check boxes, radio buttons, etc. To get your first look at a Windows Form, do the following.

If you still have your Console Application open from the previous section, click File from the menu bar at the top of Visual C# Express. From the File menu, click on Close Solution.

To create your first Windows form project, click the File menu again. This time, select New Projectfrom the menu. When you do, you'll see the New Project dialogue box again:

Or this one in C# 2010

In Visual Studio Express 2012, click Visual C#, under Templates on the left:

In all versions, select Windows Forms Application (or Windows Application in earlier versions) from the available templates. Keep the Name on the default of WindowsFormsApplication1 and then click OK.

When you click OK, a new Windows Application project will be created for you:

The obvious difference from the Console Application you created in the previous section is the blank Form in the main window. Notice the Toolbox, though, on the left hand side. We'll be adding controls from the Toolbox to that blank Form1 you can see in the image above.
If you can't see the Toolbox, you may just see the Tab, as in the following image:

In C# 2010, your screen will look like this:

If your screen looks like the one above, move your mouse over to the Toolbox tab. It will expand to look like the first one. If you want to permanently display the Toolbox, click on the pin symbol:

Notice the Solution Explorer on the right side of your screen. (If you can't see the Solution Explorer, click its entry on the View menu at the top of Visual C# Express.) If you compare it with the Solution Explorer when you created your Console Application, you'll see there's only one difference - the Form.

We still have the Properties, the References and the Program.cs file. Double click the Program.cs file to open it, and you'll see some familiar code:

And here's the code from the Console Application:

Both have the same using lines, a namespace, a class called Program, and a Main Method.
The Main Method is the entry point for your programme. The code between the curly brackets of Main will get executed when the programme first starts. The last line in the WindowsApplication1 code above is the one that Runs Form1 when the Application starts.
You can do other things here. For example, suppose you had a programme that connects to a server. If it finds a connection then it loads some information from a database. In the Main Method, you could check that the server connection is OK. If it's not, display a second form; if it's OK, then display the first form.
But don't worry if all that code has you scratching your head. The thing to bear in mind here is that a method called Main starts your programme. And Program.cs in the Solution Explorer on the right is where the code for Main lives.
But we won't be writing code in the Program.cs file, so we can close it. Have a look near the top of the coding window, and you'll some tabs:

Right click the Program.cs tab and select Close from the menu that appears. You should now see your form again (you may have a Start tab as well. You can close this, if you want).

To see the window where you'll write most of your code, right click Form1.cs in the Solution Explorer:

The menu has options for View Code and View Designer. The Designer is the Form you can see at the moment. Click View Code from the menu to see the following window appear (you can also press the F7 key on your keyboard in earlier versions, and CTRL + ALT + 0 in version 2012):

This is the code for the Form itself. This Form (screenshot from version 2008):

The code has a lot more using statements than before. Don't worry about these for now. They just mean "using some code that's already been written".
The code also says partial class Form1. It's partial because some code is hidden from you. To see the rest of it (which we don't need to alter), click the plus symbol next to Form1.cs in the Solution Explorer

Now double click Form1.Designer.cs. You'll see the following code:

Again, you see partial class Form1, which is the rest of the code. Click the plus symbol next toWindows Form Designer generated code. You'll see the following:

InitializeComponent is code (a Method) that is automatically generated for you when you create a new Windows Application project. As you add things like buttons and text boxes to your form, more code will be added here for you.
But you don't need to do anything in this window, so you can right click the Form1.Designer.cs tab at the top, and click Close from the menu.
Click back on the Form1.cs tab at the top to see you form again. If the tab is not there, right click Form1.cs in the Solution Explorer on the right. From the menu, select View Designer. Here's what you should be looking at:

t's in Designer view that we'll be adding things like buttons and text boxes to our form. But you can run this programme as it is. From the Debug menu at the top, click Start Debugging (Or you can just press the F5 key on your keyboard.):

When you click Start Debugging, Visual C# will Build the programme first, and then run it, if it can. If it can't run your programme you'll see error messages.
But you should see your form running on top of Visual Studio. It will have its own Red X, and it's own minimize and maximize buttons. Click the Red X to close your programme, and to return to Visual C# Express.
From now on, when we say Run your programme, this is what we mean: either press F5, or clickDebug > Start Debugging.
OK, time for you to start adding things to the form, and to do a little coding!

Getting Started with C# .NET

What we're going to do first is to create a very simple programme, so that you can see what makes up a C# .NET project. By the end of this chapter, you'll have learnt the following:

• How to create new projects
• What the Solution Explorer is
• The various files that make up of a C# .NET project
• How to save your work
• How to run programmes
• The importance of the Main statement

The simple programme we'll create is called a Console Application. We won't be doing much else with this type of application, as this is a book about Windows Applications. Off we go then!

Open the Visual C# Express software from your programs menu. When you first open C# (pronounced C Sharp), you should see a screen something like this (screenshot is for 2008 version, but 2005 version is the same):

Click here to see the image in a new popup window (86K)

If you have the 2010 version of Visual C# Express then your screen looks like this:

Click here to see the image in a new popup window (37K)

If you have Visual Studio Express 2012, your opening screen will look like this:

C# .NET 2012 ( new popup window - 40K )

When you're looking at this piece of software for the first time, it can seem hugely complex and daunting. The temptation is to think you're never going to get to grips with something so difficult. But don't worry - after a few lessons things will start to feel familiar, and you won't feel nearly half as intimidated as you do now!

A Simple C# Console Application

A Console Application is one that looks like a DOS window. If you don't know what these are, click your Start menu in the bottom left of your screen. Click on Run. From the dialogue box that appears, type cmd:

In Vista and Windows 7, type cmd in the search box at the bottom of the start menu. In Windows 8, the search box is on the Start Screen page. You'll then see the search results appear:

Click cmd.exe to see the console appear.

Click OK and you'll see a black screen, like this one:

This is the type of window you'll see for our Console Application. When you create your Windows forms, there's a whole lot of code to get used to. But Console Applications start off fairly simple, and you can see which part of the programme is the most important.

So with Visual C# Express open, click File from the menu bar at the top. From the File menu, selectNew Project (or click the New Project link on the left of the opening screen in versions 2010 and 2012):

When you click on New Project, you'll see the following dialogue box appear:

Or this one in version 2010 of the software:

For 2012 users, click on Templates from the list on the left. Under Templates, click on Visual C#. You'll then see Console Application appear in the middle:

For all versions, the New Project dialogue box is where you select the type of project you want to create. If you only have the Express edition of Visual C#, the options are limited. For the rest of this book, we'll be creating Windows Applications. For now, select Console Application. Then click OK.

When you click OK, a new Console Application project will be created for you. Some code should be displayed:

As well as the code, have a look on the right hand side and you'll see the Solution Explorer. This is where all the files for your project are. (If you can't see the Solution Explorer, click View from the C# menu bar at the top. From the View menu, click Solution Explorer.)
The code itself will look very complicated, if you're new to programming. We'll get to it shortly. For now, right click the Program.cs tab at the top, and click Close from the menu that appears

Or just click the X in C# 2010 and 2012

Now double click the Program.cs file in the Solution Explorer

When you double click Program.cs, you should see the code reappear. So this code is the programme that will run when anyone starts your application.
Now click the plus symbol (arrow symbol in version 2012) next to Properties in the Solution Explorer above. You'll see the following:

The file called AssemblyInfo.cs contains information about your programme. Double click this file to open it up and see the code. Here's just some of it:

The reddish colour text is something you can change. You can add a Title, Description, Copyright, Trademark, etc.

But right click the AssemblyInfo.cs tab at the top, and click Close from the menu. Now, in the Solution Explorer, click the plus symbol next to References:

These are references to code built in to C# (you won't see as many entries in earlier versions of the software). Much later, you'll see how to add your own files to this section.