input string was not in correct format

Question

i have a webforms app using asp/C# .net with SQL server 2008. i have a login form that will authenticate access to my webform website. here is the code.

SqlConnection an = new SqlConnection(@"Data Source=REZRTECH\SQLEXPRESS;Initial Catalog=Temp;Integrated Security=True");
            an.Open();
            SqlCommand anc = new SqlCommand();
            anc.Connection = an;
            anc.CommandText = "Select * From Logins where User_name = @usr";
            anc.Parameters.AddWithValue("@usr", TextBox1.Text);



            int count = Convert.ToInt32(anc.ExecuteScalar());//throws input string was not in correct format exception.
            if (count == 0)
                {
                    string swa = "User Does Not Exist";
                    ClientScript.RegisterStartupScript(this.GetType(), "myalert", "alert('" + swa + "');", true);
                    return;                      
                }
                else
                {
                 //
                    //if user name and password match goto homepage
                    {
                        Response.Redirect("~/Default.aspx");
                    }
                    else
                    {
                        string swa1 = "Invalid Login Credentials";
                        ClientScript.RegisterStartupScript(this.GetType(), "myalert", "alert('" + swa1 + "');", true);
                    }

my table rows are both nvarchar. there is one other thing that is puzzling me, one user_name is admin and its corresponding password is also admin. suppose i enter any thing other than admin, it successfully gives me the error that user is not present. that time the " input string exception is not thrown"

any and all help is appreciated.

Answer 1

The exception is happening because you are using ExecuteScalar --designed to return only a single value--and expecting that value to be an Int32 when it isn't. It seems your goal is to determine if the user is valid.

anc.CommandText = "select cast(count(1) as bit) from Logins where User_name = @usr";

then later, change int count = ... to bool isUserValid = (bool)anc.ExecuteScalar() .

Using bool instead of int count is a bit more descriptive and maintainable. There's no use in retrieving the count if you don't intend to use the count for something.

Answer 2

I Suspect that you want to get the total Count of users with the given UserName . if you want to get the Count you need to follow the follwoing SELECT command Syntax:

SELECT COUNT(*) from [TableName] WHERE CNDITION;

SO you are missing Count(*) in your SELECT Statetement.

Replace This:

anc.CommandText = "Select * From Logins where User_name = @usr";

With This:

anc.CommandText = "Select count(*) From Logins where User_name = @usr";