Tutorial: Create a .NET class library using Visual Studio

Start Visual Studio.

On the start window, choose Create a new project.

On the Create a new project page, enter solution in the search box. Choose the Blank Solution template, and then choose Next.

On the Configure your new project page, enter ClassLibraryProjects in the Solution name box. Then choose Create.

Add a new .NET class library project named "StringLibrary" to the solution.

1. Right-click on the solution in Solution Explorer and select Add > New Project.

2. On the Add a new project page, enter library in the search box. Choose C# or Visual Basic from the Language list, and then choose All platforms from the Platform list. Choose the Class Library template, and then choose Next.

3. On the Configure your new project page, enter StringLibrary in the Project name box, and then choose Next.

4. On the Additional information page, select .NET 8, and then choose Create.

Check to make sure that the library targets the correct version of .NET. Right-click on the library project in Solution Explorer, and then select Properties. The Target Framework text box shows that the project targets .NET 8.0.

If you're using Visual Basic, clear the text in the Root namespace text box.

For each project, Visual Basic automatically creates a namespace that corresponds to the project name. In this tutorial, you define a top-level namespace by using the namespace keyword in the code file.

Replace the code in the code window for Class1.cs or Class1.vb with the following code, and save the file. If the language you want to use isn't shown, change the language selector at the top of the page.

namespace UtilityLibraries;

public static class StringLibrary
{
    public static bool StartsWithUpper(this string? str)
    {
        if (string.IsNullOrWhiteSpace(str))
            return false;

        char ch = str[0];
        return char.IsUpper(ch);
    }
}

Imports System.Runtime.CompilerServices

Namespace UtilityLibraries
    Public Module StringLibrary
        <Extension>
        Public Function StartsWithUpper(str As String) As Boolean
            If String.IsNullOrWhiteSpace(str) Then
                Return False
            End If

            Dim ch As Char = str(0)
            Return Char.IsUpper(ch)
        End Function
    End Module
End Namespace

The class library, UtilityLibraries.StringLibrary, contains a method named StartsWithUpper. This method returns a Boolean value that indicates whether the current string instance begins with an uppercase character. The Unicode standard distinguishes uppercase characters from lowercase characters. The Char.IsUpper(Char) method returns true if a character is uppercase.

StartsWithUpper is implemented as an extension method so that you can call it as if it were a member of the String class. The question mark (?) after string in the C# code indicates that the string may be null.

On the menu bar, select Build > Build Solution or press Ctrl+Shift+B to verify that the project compiles without error.

Add a new .NET console application named "ShowCase" to the solution.

1. Right-click on the solution in Solution Explorer and select Add > New project.

2. On the Add a new project page, enter console in the search box. Choose C# or Visual Basic from the Language list, and then choose All platforms from the Platform list.

3. Choose the Console Application template, and then choose Next.

4. On the Configure your new project page, enter ShowCase in the Project name box. Then choose Next.

5. On the Additional information page, select .NET 8 in the Framework box. Then choose Create.

In the code window for the Program.cs or Program.vb file, replace all of the code with the following code.

using UtilityLibraries;

class Program
{
    static void Main(string[] args)
    {
        int row = 0;

        do
        {
            if (row == 0 || row >= 25)
                ResetConsole();

            string? input = Console.ReadLine();
            if (string.IsNullOrEmpty(input)) break;
            Console.WriteLine($"Input: {input}");
            Console.WriteLine("Begins with uppercase? " +
                 $"{(input.StartsWithUpper() ? "Yes" : "No")}");
            Console.WriteLine();
            row += 4;
        } while (true);
        return;

        // Declare a ResetConsole local method
        void ResetConsole()
        {
            if (row > 0)
            {
                Console.WriteLine("Press any key to continue...");
                Console.ReadKey();
            }
            Console.Clear();
            Console.WriteLine($"{Environment.NewLine}Press <Enter> only to exit; otherwise, enter a string and press <Enter>:{Environment.NewLine}");
            row = 3;
        }
    }
}

Imports UtilityLibraries

Module Program
    Dim row As Integer = 0

    Sub Main()
        Do
            If row = 0 OrElse row >= 25 Then ResetConsole()

            Dim input As String = Console.ReadLine()
            If String.IsNullOrEmpty(input) Then Return

            Console.WriteLine($"Input: {input} {"Begins with uppercase? ",30}: " +
                              $"{If(input.StartsWithUpper(), "Yes", "No")} {Environment.NewLine}")
            row += 3
        Loop While True
    End Sub

    Private Sub ResetConsole()
        If row > 0 Then
            Console.WriteLine("Press any key to continue...")
            Console.ReadKey()
        End If   
        Console.Clear()
        Console.WriteLine($"{Environment.NewLine}Press <Enter> only to exit; otherwise, enter a string and press <Enter>:{Environment.NewLine}")
        row = 3  
    End Sub
End Module

The code uses the row variable to maintain a count of the number of rows of data written to the console window. Whenever it's greater than or equal to 25, the code clears the console window and displays a message to the user.

The program prompts the user to enter a string. It indicates whether the string starts with an uppercase character. If the user presses the Enter key without entering a string, the application ends, and the console window closes.

In Solution Explorer, right-click the ShowCase project's Dependencies node, and select Add Project Reference.

In the Reference Manager dialog, select the StringLibrary project, and select OK.

In Solution Explorer, right-click the ShowCase project and select Set as StartUp Project in the context menu.

Press Ctrl+F5 to compile and run the program without debugging.

Try out the program by entering strings and pressing Enter, then press Enter to exit.

Start Visual Studio.

On the start window, choose Create a new project.

On the Create a new project page, enter solution in the search box. Choose the Blank Solution template, and then choose Next.

On the Configure your new project page, enter ClassLibraryProjects in the Solution name box. Then choose Create.

Add a new .NET class library project named "StringLibrary" to the solution.

1. Right-click on the solution in Solution Explorer and select Add > New Project.

2. On the Add a new project page, enter library in the search box. Choose C# or Visual Basic from the Language list, and then choose All platforms from the Platform list. Choose the Class Library template, and then choose Next.

3. On the Configure your new project page, enter StringLibrary in the Project name box, and then choose Next.

4. On the Additional information page, select .NET 7 (Standard-term support), and then choose Create.

Check to make sure that the library targets the correct version of .NET. Right-click on the library project in Solution Explorer, and then select Properties. The Target Framework text box shows that the project targets .NET 7.0.

If you're using Visual Basic, clear the text in the Root namespace text box.

For each project, Visual Basic automatically creates a namespace that corresponds to the project name. In this tutorial, you define a top-level namespace by using the namespace keyword in the code file.

Replace the code in the code window for Class1.cs or Class1.vb with the following code, and save the file. If the language you want to use isn't shown, change the language selector at the top of the page.

namespace UtilityLibraries;

public static class StringLibrary
{
    public static bool StartsWithUpper(this string? str)
    {
        if (string.IsNullOrWhiteSpace(str))
            return false;

        char ch = str[0];
        return char.IsUpper(ch);
    }
}

Imports System.Runtime.CompilerServices

Namespace UtilityLibraries
    Public Module StringLibrary
        <Extension>
        Public Function StartsWithUpper(str As String) As Boolean
            If String.IsNullOrWhiteSpace(str) Then
                Return False
            End If

            Dim ch As Char = str(0)
            Return Char.IsUpper(ch)
        End Function
    End Module
End Namespace

The class library, UtilityLibraries.StringLibrary, contains a method named StartsWithUpper. This method returns a Boolean value that indicates whether the current string instance begins with an uppercase character. The Unicode standard distinguishes uppercase characters from lowercase characters. The Char.IsUpper(Char) method returns true if a character is uppercase.

StartsWithUpper is implemented as an extension method so that you can call it as if it were a member of the String class. The question mark (?) after string in the C# code indicates that the string may be null.

On the menu bar, select Build > Build Solution or press Ctrl+Shift+B to verify that the project compiles without error.

Add a new .NET console application named "ShowCase" to the solution.

1. Right-click on the solution in Solution Explorer and select Add > New project.

2. On the Add a new project page, enter console in the search box. Choose C# or Visual Basic from the Language list, and then choose All platforms from the Platform list.

3. Choose the Console Application template, and then choose Next.

4. On the Configure your new project page, enter ShowCase in the Project name box. Then choose Next.

5. On the Additional information page, select .NET 7 (Standard-term support) in the Framework box. Then choose Create.

In the code window for the Program.cs or Program.vb file, replace all of the code with the following code.

using UtilityLibraries;

class Program
{
    static void Main(string[] args)
    {
        int row = 0;

        do
        {
            if (row == 0 || row >= 25)
                ResetConsole();

            string? input = Console.ReadLine();
            if (string.IsNullOrEmpty(input)) break;
            Console.WriteLine($"Input: {input}");
            Console.WriteLine("Begins with uppercase? " +
                 $"{(input.StartsWithUpper() ? "Yes" : "No")}");
            Console.WriteLine();
            row += 4;
        } while (true);
        return;

        // Declare a ResetConsole local method
        void ResetConsole()
        {
            if (row > 0)
            {
                Console.WriteLine("Press any key to continue...");
                Console.ReadKey();
            }
            Console.Clear();
            Console.WriteLine($"{Environment.NewLine}Press <Enter> only to exit; otherwise, enter a string and press <Enter>:{Environment.NewLine}");
            row = 3;
        }
    }
}

Imports UtilityLibraries

Module Program
    Dim row As Integer = 0

    Sub Main()
        Do
            If row = 0 OrElse row >= 25 Then ResetConsole()

            Dim input As String = Console.ReadLine()
            If String.IsNullOrEmpty(input) Then Return

            Console.WriteLine($"Input: {input} {"Begins with uppercase? ",30}: " +
                              $"{If(input.StartsWithUpper(), "Yes", "No")} {Environment.NewLine}")
            row += 3
        Loop While True
    End Sub

    Private Sub ResetConsole()
        If row > 0 Then
            Console.WriteLine("Press any key to continue...")
            Console.ReadKey()
        End If   
        Console.Clear()
        Console.WriteLine($"{Environment.NewLine}Press <Enter> only to exit; otherwise, enter a string and press <Enter>:{Environment.NewLine}")
        row = 3  
    End Sub
End Module

The code uses the row variable to maintain a count of the number of rows of data written to the console window. Whenever it's greater than or equal to 25, the code clears the console window and displays a message to the user.

The program prompts the user to enter a string. It indicates whether the string starts with an uppercase character. If the user presses the Enter key without entering a string, the application ends, and the console window closes.

In Solution Explorer, right-click the ShowCase project's Dependencies node, and select Add Project Reference.

In the Reference Manager dialog, select the StringLibrary project, and select OK.

In Solution Explorer, right-click the ShowCase project and select Set as StartUp Project in the context menu.

Press Ctrl+F5 to compile and run the program without debugging.

Try out the program by entering strings and pressing Enter, then press Enter to exit.

Start Visual Studio.

On the start window, choose Create a new project.

On the Create a new project page, enter solution in the search box. Choose the Blank Solution template, and then choose Next.

On the Configure your new project page, enter ClassLibraryProjects in the Solution name box. Then choose Create.

Add a new .NET class library project named "StringLibrary" to the solution.

1. Right-click on the solution in Solution Explorer and select Add > New Project.

2. On the Add a new project page, enter library in the search box. Choose C# or Visual Basic from the Language list, and then choose All platforms from the Platform list. Choose the Class Library template, and then choose Next.

3. On the Configure your new project page, enter StringLibrary in the Project name box, and then choose Next.

4. On the Additional information page, select .NET 6 (Long-term support), and then choose Create.

Check to make sure that the library targets the correct version of .NET. Right-click on the library project in Solution Explorer, and then select Properties. The Target Framework text box shows that the project targets .NET 6.0.

If you're using Visual Basic, clear the text in the Root namespace text box.

For each project, Visual Basic automatically creates a namespace that corresponds to the project name. In this tutorial, you define a top-level namespace by using the namespace keyword in the code file.

Replace the code in the code window for Class1.cs or Class1.vb with the following code, and save the file. If the language you want to use isn't shown, change the language selector at the top of the page.

namespace UtilityLibraries;

public static class StringLibrary
{
    public static bool StartsWithUpper(this string? str)
    {
        if (string.IsNullOrWhiteSpace(str))
            return false;

        char ch = str[0];
        return char.IsUpper(ch);
    }
}

Imports System.Runtime.CompilerServices

Namespace UtilityLibraries
    Public Module StringLibrary
        <Extension>
        Public Function StartsWithUpper(str As String) As Boolean
            If String.IsNullOrWhiteSpace(str) Then
                Return False
            End If

            Dim ch As Char = str(0)
            Return Char.IsUpper(ch)
        End Function
    End Module
End Namespace

The class library, UtilityLibraries.StringLibrary, contains a method named StartsWithUpper. This method returns a Boolean value that indicates whether the current string instance begins with an uppercase character. The Unicode standard distinguishes uppercase characters from lowercase characters. The Char.IsUpper(Char) method returns true if a character is uppercase.

StartsWithUpper is implemented as an extension method so that you can call it as if it were a member of the String class. The question mark (?) after string in the C# code indicates that the string may be null.

On the menu bar, select Build > Build Solution or press Ctrl+Shift+B to verify that the project compiles without error.

Add a new .NET console application named "ShowCase" to the solution.

1. Right-click on the solution in Solution Explorer and select Add > New project.

2. On the Add a new project page, enter console in the search box. Choose C# or Visual Basic from the Language list, and then choose All platforms from the Platform list.

3. Choose the Console Application template, and then choose Next.

4. On the Configure your new project page, enter ShowCase in the Project name box. Then choose Next.

5. On the Additional information page, select .NET 6 (Long-term support) in the Framework box. Then choose Create.

In the code window for the Program.cs or Program.vb file, replace all of the code with the following code.

using UtilityLibraries;

class Program
{
    static void Main(string[] args)
    {
        int row = 0;

        do
        {
            if (row == 0 || row >= 25)
                ResetConsole();

            string? input = Console.ReadLine();
            if (string.IsNullOrEmpty(input)) break;
            Console.WriteLine($"Input: {input}");
            Console.WriteLine("Begins with uppercase? " +
                 $"{(input.StartsWithUpper() ? "Yes" : "No")}");
            Console.WriteLine();
            row += 4;
        } while (true);
        return;

        // Declare a ResetConsole local method
        void ResetConsole()
        {
            if (row > 0)
            {
                Console.WriteLine("Press any key to continue...");
                Console.ReadKey();
            }
            Console.Clear();
            Console.WriteLine($"{Environment.NewLine}Press <Enter> only to exit; otherwise, enter a string and press <Enter>:{Environment.NewLine}");
            row = 3;
        }
    }
}

Imports UtilityLibraries

Module Program
    Dim row As Integer = 0

    Sub Main()
        Do
            If row = 0 OrElse row >= 25 Then ResetConsole()

            Dim input As String = Console.ReadLine()
            If String.IsNullOrEmpty(input) Then Return

            Console.WriteLine($"Input: {input} {"Begins with uppercase? ",30}: " +
                              $"{If(input.StartsWithUpper(), "Yes", "No")} {Environment.NewLine}")
            row += 3
        Loop While True
    End Sub

    Private Sub ResetConsole()
        If row > 0 Then
            Console.WriteLine("Press any key to continue...")
            Console.ReadKey()
        End If   
        Console.Clear()
        Console.WriteLine($"{Environment.NewLine}Press <Enter> only to exit; otherwise, enter a string and press <Enter>:{Environment.NewLine}")
        row = 3  
    End Sub
End Module

The code uses the row variable to maintain a count of the number of rows of data written to the console window. Whenever it's greater than or equal to 25, the code clears the console window and displays a message to the user.

The program prompts the user to enter a string. It indicates whether the string starts with an uppercase character. If the user presses the Enter key without entering a string, the application ends, and the console window closes.

In Solution Explorer, right-click the ShowCase project's Dependencies node, and select Add Project Reference.

In the Reference Manager dialog, select the StringLibrary project, and select OK.

In Solution Explorer, right-click the ShowCase project and select Set as StartUp Project in the context menu.

Press Ctrl+F5 to compile and run the program without debugging.

Try out the program by entering strings and pressing Enter, then press Enter to exit.