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 Studio. From the File menu, click
Close Solution. Start a new project by clicking File again,
then New Project. From the New Project dialogue box, select Windows
Forms Application. In the Name box, type String 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
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 under Common 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
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#.
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