How do I use a try and catch block in vb.net? [closed]

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For the code shown below, how would I use a try/catch block to handle an error if it were to occur?

        TOTKILO.Text = KILO.Text * TOUCH.Text * 0.01
        TextBox10.Text = TextBox9.Text * TextBox8.Text * 0.01
        K = Math.Round(Val(TOTKILO.Text) - Val(TextBox10.Text), 5)
        TextBox11.Text = TextBox7.Text + K

        cmd.CommandType = Data.CommandType.Text
        con.ConnectionString = "Data Source=.\SQLEXPRESS;AttachDbFilename=C:\Documents and Settings\Administrator\My Documents\Visual Studio 2005\Projects\SHOPPROJECT\SHOPPROJECT\shop.mdf;Integrated Security=True;User Instance=True"
        con.Open()
        If RadioButton1.Checked Then
            GOLD = 1
        ElseIf RadioButton2.Checked Then
            SILVER = 1
        End If
        If RadioButton3.Checked Then
            KGOLD = 1
        Else开发者_JAVA百科If RadioButton4.Checked Then
            KSILVER = 1
        End If
        cmd.CommandText = " INSERT INTO SALES VALUES('" & ComboBox1.Text & " ' , " & SILVER & " ," & GOLD & ",'" & ComboBox2.Text & "'," & KILO.Text & ", " & TOUCH.Text & " ," & TOTKILO.Text & "," & TextBox3.Text & "," & TextBox8.Text & "," & KGOLD & "," & KSILVER & "," & TextBox9.Text & " ," & TextBox10.Text & "," & TextBox11.Text & "," & TextBox12.Text & " , " & TextBox13.Text & " ) "
        cmd.CommandType = " UPDATE BALANCE SET OBBALANCE = " & TextBox11.Text & " WHERE CUSTOMERNAME = '" & ComboBox1.Text & "' "
        cmd.Connection = con
        cmd.ExecuteNonQuery()
        con.Close()
END SUB

I used VB.Net controls and LINQ to SQL to perform all Updates and Inserts, so when an error occurs I want to show "Enter Data Correctly", how do I do that once I catch an exception?

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I have added a simple Try...Catch below, but I think you will find you have a lot of issues:

• You appear to be doing multiplication on string objects, you should parse out the numbers first then cast back to string objects as necessary.
• You are also setting CommandType twice and in the second instance to an update command rather than an appropriate value.
• Your code is wide open to SQL injection, you should not be building your SQL statements through string concatenation, but rather using sqlparameters
• If you are going to do string concatenation at least use a string builder, but don't do string concatenation (see above)
• Disposable objects (like SQLCommand) need to be placed in Using blocks
• Don't post in all caps
• Only post your question once, you can edit a question once you've posted it if you'd like to add detail

Here is the modifed code:

Try
    TOTKILO.Text = KILO.Text * TOUCH.Text * 0.01
    TextBox10.Text = TextBox9.Text * TextBox8.Text * 0.01
    K = Math.Round(Val(TOTKILO.Text) - Val(TextBox10.Text), 5)
    TextBox11.Text = TextBox7.Text + K
    cmd.CommandType = Data.CommandType.Text
    con.ConnectionString = "Data Source=.\SQLEXPRESS;AttachDbFilename=C:\Documents and Settings\Administrator\My Documents\Visual Studio 2005\Projects\SHOPPROJECT\SHOPPROJECT\shop.mdf;Integrated Security=True;User Instance=True"
    con.Open()
    If RadioButton1.Checked Then
        GOLD = 1
    ElseIf RadioButton2.Checked Then
        SILVER = 1
    End If
    If RadioButton3.Checked Then
        KGOLD = 1
    ElseIf RadioButton4.Checked Then
        KSILVER = 1
    End If
    cmd.CommandText = " INSERT INTO SALES VALUES('" & ComboBox1.Text & " ' , " & SILVER & " ," & GOLD & ",'" & ComboBox2.Text & "'," & KILO.Text & ", " & TOUCH.Text & " ," & TOTKILO.Text & "," & TextBox3.Text & "," & TextBox8.Text & "," & KGOLD & "," & KSILVER & "," & TextBox9.Text & " ," & TextBox10.Text & "," & TextBox11.Text & "," & TextBox12.Text & " , " & TextBox13.Text & " ) "
    cmd.CommandType = " UPDATE BALANCE SET OBBALANCE = " & TextBox11.Text & " WHERE CUSTOMERNAME = '" & ComboBox1.Text & "' "
    cmd.Connection = con
    cmd.ExecuteNonQuery()
Catch (ex as Exception)
    MsgBox.Show("Enter Data Correctly: " & ex.toString)
Finally
    con.Close()
End Try