Visual Basic .NET

Char and Chars in VB .NET

Char ( NOT Chars)

Char is a variable type. It can hold one character at a time (the Char
is short for Character). You set it up like this:

Dim OneCharacter As Char

You can then store a character in the variable like this:

OneCharacter = “A”

Or like this:

Dim OneCharacter As Char = “a”

You can even do this:

Dim OneCharacter As Char = “apple”

But if you try to put a whole word into a Char variable, only the first letter
will be retained.

So what good is the Char variable type?

Well, a common use for it is to transfer one letter at a time from a string,
and then test to see what this character is. You can test to see if it’s a number,
for example. Or perhaps to test if the string contains an “@” symbol
for a valid email address. We’ll test for a number. In the process, we can study
the Length property of string variables.

Add another textbox and a button to your form from the first
part of the tutorial. Change the Name property of the textbox to
txtChars. For the Text property of the Textbox, enter “George123“.
Double click the new button and enter the following variable declarations:

Dim OneCharacter As Char
Dim FirstName As String
Dim i As Integer
Dim TextLength As Integer

Remember what we’re going to be doing here. We’re going to put the text from
the textbox into a string variable. Then we’ll loop round every character in
the string to see if it’s a number.

So the next line to add to your code is the one that transfers the text from
the textbox to the string variable. Add this:

FirstName = Trim(txtChars.Text)

The next thing we need is the length of the string. We need this for the end
value of our loop. The length property will give us this answer. So add this
line:

TextLength = FirstName.Length

The length property of a string variable tells you how many characters are
in the string. You can add a message box to test out your code so far:

MessageBox.Show(“Number of characters is: ”
& TextLength)

Run your programme. Click the button and test out your code. You should see
a message box popping up like this one:

Message Box showing the length of a string

So we’ve found out that “George123” has 9 characters.

We can now loop round each character in the string and test which ones are
the numbers. Add the following For loop to your code (you can delete or comment
out your message box line now):

For i = 0 To TextLength – 1

Next i

So the For loop starts at zero and ends at the length of the text, minus 1.
(It will loop from 0 to 8 in our code – 9 characters. We’ll see why you have
to deduct 1 soon.

Inside of our loop, we need to grab one character at a time, and then put it
into our Char variable. You can do that with the Chars() Property
of the string variable type.

Chars (NOT Char)

Chars is a method of the String variable type. You can use it on any
length of string, not just a Char variable. And that’s the difference between
the two: Char is a variable type, while Chars is a method you can use
on Strings.

Chars works like this:

OneCharacter = FirstName.Chars(i)

You type the name of your variable, then after the full stop you add Chars().
Inside of the round brackets, you need a number. This number is the position
in the string you want to grab. So if you wanted the third letter of a string
variable, you’d put this:

Dim SomeString As String
Dim OneCharacter As Char

SomeString = “George123”
OneCharacter = SomeString.Chars(2)

The variable OneCharacter would then hold the third letter – “o“.

The reason we’ve put 2 inside of the round brackets and not 3 is because VB
starts counting the characters from zero, and NOT 1. And that’s why our For
Loop is this:

For i = 0 To TextLength – 1

You have to deduct 1 because the Chars() count starts at zero.

So amend your For Loop to this:

For i = 0 To TextLength – 1

OneCharacter = FirstName.Chars(i)
MessageBox.Show(OneCharacter)

Next i

Run your code, and then click your button. You should get a message box displaying.
In fact, you’ll get 9 message boxes, one for each character in the string!

Ok, try these exercises to test your new knowledge.

Exercise K

Add an If statement to your For Loop. Check each character of the string “George123“.
If you find a number, display a suitable message, something like “A number
was found”. Exit the for loop when the first number is found.

To check if a variable is a number, you can use the IsNumeric( ) function.
This function will return either True or False. In other words, if the variable
being checked is a number, then IsNumeric( ) is True; if IsNumeric( ) is not
a number then False gets returned.

If IsNumeric(OneCharacter) Then

Exercise L

Amend your code to keep a count of how many characters in the string are numbers.
Display the count in a message box.

In the next part, we’ll take a look at another useful String method – InStr.

Kaynak : https://www.homeandlearn.co.uk/NET/nets7p3.html ‘sitesinden alıntı

Yorum Yap