Tutorial: Learn to debug Visual Basic code using Visual Studio

Applies to: Visual Studio Visual Studio for Mac

This article introduces the features of the Visual Studio debugger in a step-by-step walkthrough. If you want a higher-level view of the debugger features, see First look at the debugger. When you debug your app, it usually means that you are running your application with the debugger attached. When you do this, the debugger provides many ways to see what your code is doing while it runs. You can step through your code and look at the values stored in variables, you can set watches on variables to see when values change, you can examine the execution path of your code, see whether a branch of code is running, and so on. If this is the first time that you've tried to debug code, you may want to read Debugging for absolute beginners before going through this article.

Although the demo app is Visual Basic, most of the features are applicable to C#, C++, F#, Python, JavaScript, and other languages supported by Visual Studio (F# does not support Edit-and-continue. F# and JavaScript do not support the Autos window). The screenshots are in Visual Basic.

In this tutorial, you will:

Prerequisites

Create a project

First, you'll create a .NET Core console application project. The project type comes with all the template files you'll need, before you've even added anything!

Create the application

1. In Program.vb, replace all of the default code with the following code instead:

   Imports System
   
   Class ArrayExample
       Public Shared Sub Main()
           Dim letters As Char() = {"f"c, "r"c, "e"c, "d"c, " "c, "s"c, "m"c, "i"c, "t"c, "h"c}
           Dim name As String = ""
           Dim a As Integer() = New Integer(9) {}
   
           For i As Integer = 0 To letters.Length - 1
               name += letters(i)
               a(i) = i + 1
               SendMessage(name, a(i))
           Next
   
           Console.ReadKey()
       End Sub
   
       Private Shared Sub SendMessage(ByVal name As String, ByVal msg As Integer)
           Console.WriteLine("Hello, " & name & "! Count to " & msg)
       End Sub
   End Class
   

Start the debugger!

Set a breakpoint and start the debugger

Navigate code in the debugger using step commands

Navigate code using Run to Click

Restart your app quickly

Inspect variables with data tips

Inspect variables with the Autos and Locals windows

Set a watch

1. In the main code editor window, right-click the name variable and choose Add Watch.

   The Watch window opens at the bottom of the code editor. You can use a Watch window to specify a variable (or an expression) that you want to keep an eye on.

   Now, you have a watch set on the name variable, and you can see its value change as you move through the debugger. Unlike the other variable windows, the Watch window always shows the variables that you are watching (they're grayed out when out of scope).

Examine the call stack

Change the execution flow

1. Press F11 twice to run the Console.WriteLine method.

2. With the debugger paused in the SendMessage method call, use the mouse to grab the yellow arrow (the execution pointer) on the left and move it up one line, back to Console.WriteLine.

3. Press F11.

   The debugger reruns the Console.WriteLine method (you see this in the console window output).

   By changing the execution flow, you can do things like test different code execution paths or rerun code without restarting the debugger.

   Warning

   Often you need to be careful with this feature, and you see a warning in the tooltip. You may see other warnings, too. Moving the pointer cannot revert your application to an earlier app state.

4. Press F5 to continue running the app.

   Congratulations on completing this tutorial!

Next steps

In this tutorial, you've learned how to start the debugger, step through code, and inspect variables. You may want to get a high-level look at debugger features along with links to more information.