Visual Studio C# Error: Input string was not in correct format

Question

Visual Studio C# Error: Input string was not in correct format

VAer-4038 776

The error shows up when running into " int count = Convert.ToInt32(cmd.ExecuteScalar())", Data Type for Access UserID is short text. What goes wrong?

Thanks.

        private void btnConnect_Click(object sender, EventArgs e)  
        {  
              
            OdbcConnection Cn = new OdbcConnection(GlobalVariables.DatabaseConnectionString);  
  
            Cn.Open();  
  
            string select = "SELECT * from TUser WHERE UserID ='" + Environment.UserName + "'";  
   
  
            using (OdbcCommand cmd = new OdbcCommand(select, Cn))  
                {  
                  
                int count = Convert.ToInt32(cmd.ExecuteScalar());  
                    if (count > 0)  
                    {  
                        MessageBox.Show("Existed!");  
                    }  
                    else  
                    {  
  
                        MessageBox.Show("No existed");  
                    }  
                //}  
            }  
  
  
        }

David Lowndes 4,726 Reputation points

2021-01-01T18:06:32.07+00:00

Split the line of code up into 2 statements so that you can easily see what cmd.ExecuteScalar() is returning - that will hopefully clarify the source of the problem.
VAer-4038 776 Reputation points

2021-01-01T18:09:30.057+00:00

Sorry, how to split into two lines? I am new to both C# and Visual Studio. I basically copied the code from this post: visual-studio-c-how-to-check-a-value-against-acces.html

Thanks.
David Lowndes 4,726 Reputation points

2021-01-01T18:15:30.293+00:00
object obj = cmd.ExecuteScalar(); int count = Convert.ToInt32(obj);
VAer-4038 776 Reputation points

2021-01-01T18:22:52.997+00:00

Yes, the error is in int count = Convert.ToInt32(obj);

In face, the access table has one record matching Environment.UserName, so the result for count should be 1.

Now how to fix the code? What is Convert.ToInt32? I believe it is 64-bit machine. Not sure if it has anything to do with it.

Thanks.
David Lowndes 4,726 Reputation points

2021-01-01T18:24:31.51+00:00

What is the value/type of "obj" when you debug it?
VAer-4038 776 Reputation points

2021-01-01T18:47:16.997+00:00

It is hard to explain. I cannot actually debug the program in my work computer (I will explain in another post, it seems to be new forum, I used to ask question under: https://social.msdn.microsoft.com/Forums/vstudio/en-US/home?forum=csharpgeneral . Maybe you post as comment here, not as answer, therefore, there is character limit for me to reply your comment).

More about Citrix virtual desktop: Citrix_Workspace
VAer-4038 776 Reputation points

2021-01-01T18:47:45.28+00:00

The work computer works like that: When I log in computer, and Visual Studio is installed in the machine. Probably due to security reason (or setting by IT, I am not an IT professional, don't know much about IT), there is restriction to run exe file in this machine, therefore I am not able to debug the program. Employees do not really work in machine desktop, instead they open the browser and login Citrix virtual desktop and do the daily work there. Citrix virtual desktop only offers some common software to employees, not including Visual Studio. If an employee needs additional software (like Visual Studio), it will need to be installed in machine desktop. That being said, I have to build application in machine desktop, then copy exe file to Citrix virtual desktop, and run the application there. Moreover, access database file is located in Citrix virtual desktop.

If there is error, I try to put MessageBox everywhere to identify which line causes the error.
David Lowndes 4,726 Reputation points

2021-01-01T18:51:38.537+00:00

You have my sympathy being so hamstrung.
You're really on a hiding to nothing if you can't debug what you're working on - have a word with your manager!
Happy New Year too.
VAer-4038 776 Reputation points

2021-01-01T18:56:30.847+00:00

It is big organization and it is kinda bureaucratic. For IT setting, I cannot really change it. However, I will try to run the code in my home computer (Community Edition) later.
Sergio Parra Guerra 1 Reputation point MVP Volunteer Moderator

2021-01-01T19:01:27.067+00:00

int count = 0;
object obj = cmd.ExecuteScalar();
if (obj =! DBNull.Value)
{
count = Convert.ToInt32(obj);
}

You should check obj before apply Convert
VAer-4038 776 Reputation points

2021-01-01T19:04:39.883+00:00

It is so strange, I copied the whole project folder to home computer, the same code (only changing Access File path) runs fine without error.

Is it because of different machines (32 bit or 64 bits)? But they are both window 10, I guess both are 64 bits.
David Lowndes 4,726 Reputation points

2021-01-01T19:07:49.247+00:00

I'd doubt it's a 32/64-bit issue - more likely an environmental difference - something failing in your work environment.
You really need to be able to debug it where the problem is showing up rather than having to guess.
VAer-4038 776 Reputation points

2021-01-01T19:11:52.137+00:00

It causes more problem. With the code update (like you suggested), there is error for if (count > 0) : CS0103 The name 'count' does not exist in the current context.

Maybe I should try to use SELECT COUNT(), but not sure how to modify the code.
Sergio Parra Guerra 1 Reputation point MVP Volunteer Moderator

2021-01-01T19:18:08.833+00:00

Sorry about that. I have edited my last answer

Answer accepted by question author

1 additional answer

Your answer

David Lowndes 4,726 Reputation points

2021-01-01T18:06:32.07+00:00

Split the line of code up into 2 statements so that you can easily see what cmd.ExecuteScalar() is returning - that will hopefully clarify the source of the problem.
VAer-4038 776 Reputation points

2021-01-01T18:09:30.057+00:00

Sorry, how to split into two lines? I am new to both C# and Visual Studio. I basically copied the code from this post: visual-studio-c-how-to-check-a-value-against-acces.html

Thanks.
David Lowndes 4,726 Reputation points

2021-01-01T18:15:30.293+00:00

object obj = cmd.ExecuteScalar(); int count = Convert.ToInt32(obj);
VAer-4038 776 Reputation points

2021-01-01T18:22:52.997+00:00

Yes, the error is in int count = Convert.ToInt32(obj);

In face, the access table has one record matching Environment.UserName, so the result for count should be 1.

Now how to fix the code? What is Convert.ToInt32? I believe it is 64-bit machine. Not sure if it has anything to do with it.

Thanks.
David Lowndes 4,726 Reputation points

2021-01-01T18:24:31.51+00:00

What is the value/type of "obj" when you debug it?
VAer-4038 776 Reputation points

2021-01-01T18:47:16.997+00:00

It is hard to explain. I cannot actually debug the program in my work computer (I will explain in another post, it seems to be new forum, I used to ask question under: https://social.msdn.microsoft.com/Forums/vstudio/en-US/home?forum=csharpgeneral . Maybe you post as comment here, not as answer, therefore, there is character limit for me to reply your comment).

More about Citrix virtual desktop: Citrix_Workspace
VAer-4038 776 Reputation points

2021-01-01T18:47:45.28+00:00

The work computer works like that: When I log in computer, and Visual Studio is installed in the machine. Probably due to security reason (or setting by IT, I am not an IT professional, don't know much about IT), there is restriction to run exe file in this machine, therefore I am not able to debug the program. Employees do not really work in machine desktop, instead they open the browser and login Citrix virtual desktop and do the daily work there. Citrix virtual desktop only offers some common software to employees, not including Visual Studio. If an employee needs additional software (like Visual Studio), it will need to be installed in machine desktop. That being said, I have to build application in machine desktop, then copy exe file to Citrix virtual desktop, and run the application there. Moreover, access database file is located in Citrix virtual desktop.

If there is error, I try to put MessageBox everywhere to identify which line causes the error.
David Lowndes 4,726 Reputation points

2021-01-01T18:51:38.537+00:00

You have my sympathy being so hamstrung.
You're really on a hiding to nothing if you can't debug what you're working on - have a word with your manager!
Happy New Year too.
VAer-4038 776 Reputation points

2021-01-01T18:56:30.847+00:00

It is big organization and it is kinda bureaucratic. For IT setting, I cannot really change it. However, I will try to run the code in my home computer (Community Edition) later.
Sergio Parra Guerra 1 Reputation point MVP Volunteer Moderator

2021-01-01T19:01:27.067+00:00

int count = 0;
object obj = cmd.ExecuteScalar();
if (obj =! DBNull.Value)
{
count = Convert.ToInt32(obj);
}

You should check obj before apply Convert
VAer-4038 776 Reputation points

2021-01-01T19:04:39.883+00:00

It is so strange, I copied the whole project folder to home computer, the same code (only changing Access File path) runs fine without error.

Is it because of different machines (32 bit or 64 bits)? But they are both window 10, I guess both are 64 bits.
David Lowndes 4,726 Reputation points

2021-01-01T19:07:49.247+00:00

I'd doubt it's a 32/64-bit issue - more likely an environmental difference - something failing in your work environment.
You really need to be able to debug it where the problem is showing up rather than having to guess.
VAer-4038 776 Reputation points

2021-01-01T19:11:52.137+00:00

It causes more problem. With the code update (like you suggested), there is error for if (count > 0) : CS0103 The name 'count' does not exist in the current context.

Maybe I should try to use SELECT COUNT(), but not sure how to modify the code.
Sergio Parra Guerra 1 Reputation point MVP Volunteer Moderator

2021-01-01T19:18:08.833+00:00

Sorry about that. I have edited my last answer

Answer 1

Viorel 125.7K

To make it work with minimal changes, try *“select ****COUNT(*)*** from…”, however this is not the only known approach.

VAer-4038 776 Reputation points

2021-01-01T18:24:12.227+00:00

Quite new to C# and Visual Studio, how should I modify the code?

Thanks.
Viorel 125.7K Reputation points

2021-01-01T18:27:36.86+00:00
Edit the above line 8:

string select = "SELECT COUNT(*) from TUser WHERE UserID ='" + Environment.UserName + "'";

Also consider “Parameterised Queries” in your next versions.
Castorix31 91,501 Reputation points

2021-01-01T18:28:23.967+00:00
ExecuteScalar returns the first column of first row
if you want a count, do like Viorel said :

string select = "SELECT count(*) from TUser WHERE UserID ='" + Environment.UserName + "'";
VAer-4038 776 Reputation points

2021-01-01T19:17:54.833+00:00

Thanks. It seems COUNT solving the problem.

It is just strange to me, without change it to COUNT, the code runs fine on my home computer (Community Edition), but it just returns the error when running on my work computer (Citrix virtual desktop), now with COUNT, it runs fine on my work computer (Citrix virtual desktop) too.

I don't know much about IT, just don't know what causes the problem.
Viorel 125.7K Reputation points

2021-01-01T19:23:05.28+00:00

Probably the username that is used on your work computer was not present in database.

Answer 2

Sergio Parra Guerra 1 MVP Volunteer Moderator

Hi! ExecuteScalar returns an object.
Sometimes it can return a DBNull representing a non-existent value, which is not casteable to Int32.

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Visual Studio C# Error: Input string was not in correct format

1 additional answer

Your answer