STRING FUNCTION
Learning Outcomes
At the end of this lecture you will be able to :
1.Compare strings
2.Manipulate characters in a string using string functions
3.Reverse a string using string functions
4.Use Instr string function to perform data validation
Key Words
1.
2.
3.
4.
5.
6.
7.
8.
StrComp
Left
Right
Mid
Trim
Len
Ucase
Instr
String Data Type
■ A string constant is a sequence of characters that is treated
as a single item
■ String data type is used to store characters
■ Strings can be concatenated (using &) for combining strings
Comparing Strings
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
lblresult.text = StrComp(txtinput1.text, txtinput2.text)
End Sub
Uses function StrComp to compare strings
Function StrComp returns :
 0 if the strings are equal
 -1 if the first string is lesser than the second string
 1 if the first string is greater than the second string
EXERCISE (Comparing Strings)
■ Write a program to accept two strings using two text boxes.
Determine if the first string is greater than the second string.
Output
B is greater than A
String Functions
■ Strings.Left is used to extract a character from the left of a string.
– Syntax: Strings.Left(String, Length)
Example: Label1.Text = Strings.Left("Mississippi", 3)
OUTPUT: Mis
■ Strings.Right is used to extract a character from the right of a string.
– Syntax: Strings.Right(String, Length)
Example: Label1.Text = Strings.Right("Mississippi", 3)
OUTPUT: ppi
■ Strings.Mid is used to extract a character from a specific position in a string.
– Syntax: Strings.Mid(String, Start, Length)
Example: Label1.Text = Strings.Mid("Mississippi", 5,2)
OUTPUT: is
■ Strings.Left is used to extract a character from the left of a string
Syntax: Strings.Left(String, Length)
Example: Label1.Text = Strings.Left(TextBox1.Text, 5)
OUTPUT : Hello
–
■ Strings.Right is used to extract a character from the right of a string
Syntax: Strings.Right(String, Length)
Example: Label1.Text = Strings.Right(TextBox1.Text, 5)
OUTPUT : World
–
■ Strings.Mid is used to extract a character from a specific position in a string
Syntax: Strings.Mid(String, Start, Length)
Example: Label1.Text = Strings.Mid(TextBox1.Text, 3, 5)
OUTPUT: llo W
–
String Functions
■ Ltrim -Removes leading spaces at the left side of a string.
– Syntax: LTrim(String)
Example: Ltrim(“_ _vb”)
OUTPUT: “vb”
■ Rtrim -Removes trailing spaces at the right side of a string.
– Syntax: RTrim(String)
Example: Rtrim(“vb_ _ _”)
OUTPUT: “vb”
■ Trim – removes spaces on both left and right of a string.
– Syntax: LTrim(String)
Example: Trim(“_ _ vb_ _”)
OUTPUT: “vb”
■ Ltrim -Removes leading spaces at the left side of a string.
–
Syntax: LTrim(String)
Example: Label1.Text = LTrim(TextBox1.Text)
OUTPUT: “Hello World ”
■ Rtrim -Removes trailing spaces at the right side of a string.
–
Syntax: RTrim(String)
Example: Label1.Text = RTrim(TextBox1.Text)
OUTPUT: “ Hello World”
■ Trim – removes spaces on both left and right of a string.
–
Syntax: Trim(String)
Example: Label1.Text = Trim(TextBox1.Text)
OUTPUT: “Hello World”
EXERCISE (String Functions)
Write a program to do the following :
a) Display the first three characters of your
name
b) Display the last three characters of you name
c) Display the letter “S” in BSIT
String Functions
■ Strings.Len - Is used to determine the length of a string.
–
Syntax: Strings.Len(String)
Example: Label1.text = Strings.Len(“Welcome”)
OUTPUT: 7
■ Strings.Ucase - Is used to convert a string to uppercase.
–
Syntax: Strings.Ucase(String)
Example: Label1.text = Strings.Ucase(“Welcome”)
OUTPUT: WELCOME
■
Strings.Lcase – Is used to convert a string to lowercase
–
Syntax: Strings.Lcase(String)
Example: Label1.text = Strings.Lcase(“Welcome”)
OUTPUT: welcome
■ Strings.Len - Is used to determine the length of a string.
–
Syntax: Strings.Len(String)
Example: Label1.text = Strings.Len(TextBox1.Text)
OUTPUT: 11
■ Strings.Ucase - Is used to convert a string to uppercase.
–
Syntax: Strings.Ucase(String)
Example: Label1.text = Strings.Ucase(TextBox1.Text)
OUTPUT: HELLO WORLD
■
Strings.Lcase – Is used to convert a string to lowercase
–
Syntax: Strings.Lcase(String)
Example: Label1.text = Strings.Lcase(TextBox1.Text)
OUTPUT: hello world
Exercise
Show the answer for the following functions:
1. Strings.Ucase(“McD’s”)
2. Strings.Left(“Pinterest”,3)
3. Strings.Mid(“Facebook”,5,4)
4. Strings.Len(“Netflix”)
5. Strings.Right(“Pinterest”,8)
6. Strings.Lcase(“TikTok”)
Exercise
Write a program that will accept a string using a
text box. Your program should display the
string in reverse order. Use a text box for
display.
Use the following string functions
 Mid
 Len
 For …Next
Reversing A String
■ Reversing a string using function StrReverse.
– Syntax: StrReverse(String)
Example: Label1.text = StrReverse(“Welcome”)
OUTPUT: emocleW
Reversing A String
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
TextBox2.Text = StrReverse(TextBox1.Text)
End Sub
OUTPUT:
InStr
■ Is used to search whether an item is found in a string
■ Used to return the position at which the content matches the
string.
–
Syntax: Instr(String)
Example: Label1.text = Instr(“Alcohol”, “o”)
OUTPUT: 4
Example: Label1.text = (“Just a moment”, “ ”)
OUTPUT: 5
Example: Label1.text = Instr(“Croissant”, “ist”)
OUTPUT: 0
InStr
The InStr( ) method of string variables tells you what the position of
one string is inside another.
For example, if your string was "me@me.com" and you wanted to
know if the string contained the @ symbol, you could use InStr( )
Method. You would use it like this
FirstString = "me@me.com"
SecondString = "@"
position = InStr( FirstString, SecondString )
InStr
The variable FirstString is the string we want to search; SecondString is what
we want to search for. You can specify a starting position for the search to
begin. If you do, this number goes at the start (the default is zero):
position = InStr( 1, FirstString, SecondString )
The variable called position has to be an integer variable. That's because
the InStr() Method returns a number, and not text. In the code
above, position would have a value of 3. That's because the @ symbols starts
at the third letter of "me@me.com".
*(Note: the InStr() Method starts counting at 1, and not zero like Chars(), which is very confusing!)
InStr
If the string you're searching for is not found, then the value placed inside
of your integer variable (position in our case) is zero. That enables you to
code something like this:
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles
Button1.Click
Label1.Text = InStr(TextBox1.Text, TextBox2.Text)
If Label1.Text = 0 Then
MessageBox.Show("Not a Valid email address: There was No @ Sign")
End If
End Sub
OUTPUT
OUTPUT
ARIGATHANKS!!! 
ANA GADON