As well as storing text in memory you can, of course, store numbers. There
are a number of ways to store numbers, and the ones you’ll learn about now are
called Integer, Double and Float. First up, though, are Integer variables.
First, close any solution you have open by clicking File > Close Solution
from the menu bar at the top of Visual Studio. Start a new project by clicking
File > New Project. From the New Project dialogue box, select Windows
Forms Application from the available templates. Type a Name for your project.
Call it Numbers.
Click OK, and you’ll have a new form to work with.
An integer is a whole number. It’s the 6 of 6.5, for example. In programming,
you’ll work with integers a lot. But they are just variables that you store
in memory and want to manipulate. You’ll now see how to set up and use Integer
Add a button to your form, and set the following properties for it in the Properties
Location: 110, 20
Now double click your button to get at the code:
In the previous section, you saw that to set up a string variable you just
You set up an integer variable in the same way. Except, instead of typing the
word string, you type the word int (short for integer).
So, in between the curly brackets of your button code, type int. You
should see the word turn blue, and the IntelliSense list appear:
Either press the enter key on your keyboard, or just hit the spacebar. Then
type a name for your new variable. Call it myInteger. Add the semi-colon
at the end of your line of code, and hit the enter key. Your coding window will
then look like this:
Notice the text in the yellow box, in the image one up from the one above.
Represents a 32-bit signed integer
A signed integer is one that can have negative values, like -5, -6, etc. (The
opposite, no negative numbers, is called an unsigned integer.) The 32-bit part
is referring to the range of numbers that an integer can hold. The maximum value
that you can store in an integer is: 2,147,483,648. The minimum value is the
same, but with a minus sign on the front: -2,147,483,648.
To store an integer number in your variable, you do the same as you did for
string: type the name of your variable, then an equals sign ( = ), then the
number you want to store. So add this line to your code (don’t forget the semi-colon
on the end):
myInteger = 25;
Your coding window should look like this:
So we’ve set up an integer variable called myInteger. On the second line, we’re
storing a value of 25 inside of the variable.
We’ll use a message box to display the result when the button is clicked. So
add this line of code for line three:
Now try to run your code. You’ll get the following error message:
You should see a wiggly line under your MessageBox code:
Hold your mouse over myInteger, between the round brackets of Show(
). You should see the following yellow box:
The error is: “Cannot convert from int to string”. The reason you
get this error is because myInteger holds a number. But the MessageBox
only displays text. C# does not convert the number to text for you. It doesn’t
do this because C# is a programming language known as “strongly typed”.
What this means is that you have to declare the type of variable you are using
(string, integer, double). C# will then check to make sure that there are no
numbers trying to pass themselves off as strings, or any text trying to pass
itself off as a number. In our code above, we’re trying to pass myInteger
off as a string. And C# has spotted it!
What you have to do is to convert one type of variable to another. You can
convert a number into a string quite easily. Type a full stop (period) after
the “r” of myInteger. You’ll see the IntelliSense list appear:
Select ToString from the list. Because ToString is a method,
you need to type a pair of round brackets after the “g” of ToString.
Your code will then look like this (we’ve highlighted the new addition):
The ToString method, as its name suggests, converts something to a string of
text. The thing we are converting is an integer.
Start your programme again. Because you’ve converted an integer to a string,
you should find that it runs OK now. Click your button and you should see the
message box appear:
In the next lesson, we’ll take a look at double variables, and float variables.
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