ToLower, ToUpper

ToLower changes Strings that contain uppercase letters. We convert all the uppercase letters in a String to lowercase letters. With ToLower this is easy to do.

We can also use ToLower to determine if a String is already lowercased. With ToUpper we uppercase a string. With special logic, we can uppercase only the first letter.

This program uses the ToLower function. In the first part, we lowercase the String "ABC123." Notice how the non-uppercase letters "123" are kept the same in the output.

Module Module1
    Sub Main()
        ' Convert string to lowercase.
        Dim value As String = "ABC123"
        value = value.ToLower()
        Console.WriteLine(value)

        ' See if a String is already lowercase.
        Dim cat As String = "cat"
        If cat = cat.ToLower() Then
            Console.WriteLine("Is Lower")
        End If
    End Sub
End Module
abc123
Is Lower

ToUpper example

ToUpper converts all characters to uppercase characters. It causes a copy to be made of the VB.NET String, which is returned.

Module Module1
    Sub Main()
        Dim value1 As String = "abc123"
        Dim upper1 As String = value1.ToUpper()
        Console.WriteLine(upper1)
    End Sub
End Module
ABC123

IsUppercase

How can you determine if a String is already uppercase? We can use ToUpper and then compare the original String. If they are equal, the string was already uppercased.

Module Module1

    Function IsUppercase(ByRef value As String) As Boolean
        ' Loop over all characters in the string.
        ' ... Return false is one is lowercase.
        '     Otherwise, return true (all letters are uppercase).
        For Each letter As Char In value
            If Char.IsLower(letter) Then
                Return False
            End If
        Next
        Return True
    End Function

    Sub Main()
        Console.WriteLine("ISUPPERCASE: {0}", IsUppercase("BIRD"))
        Console.WriteLine("ISUPPERCASE: {0}", IsUppercase("Bird"))
        Console.WriteLine("ISUPPERCASE: {0}", IsUppercase(""))
    End Sub

End Module
ISUPPERCASE: True
ISUPPERCASE: False
ISUPPERCASE: True

ToTitleCase

To use the ToTitleCase() function, we must access the TextInfo class. This is a bit more complex. In a title case string, each word starts with a capital.

Imports System.Globalization

Module Module1

    Sub Main()

        Dim value As String = "can of worms"

        ' Uppercase words with ToTitleCase.
        Dim info As TextInfo = CultureInfo.InvariantCulture.TextInfo
        Dim result As String = info.ToTitleCase(value)

        Console.WriteLine("INPUT:  {0}", value)
        Console.WriteLine("OUTPUT: {0}", result)

    End Sub

End Module
INPUT:  can of worms
OUTPUT: Can Of Worms

ToUpper function changes no characters except lowercase characters. Digits and uppercase letters (as well as punctuation and spaces) are left the same.

We looked at ToLower and ToUpper. These functions return a copy of the original string. With ToLower, all a string's uppercase letters are changed to lowercase letters.