Help with my C# Program

Question

1.00/5 (3 votes)

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Hello all

I need help with this code for an assignment, it gives me an error when trying to use the else statement.

C#

public partial class Form1 : Form
   {
       public Form1()
       {
           InitializeComponent();
       }

       //Button click event
       private void btnPredict_Click(object sender, EventArgs e)
       {


           //If statments
           if (cmbMode.SelectedItem.Equals("Flashing") && cmbColour.SelectedItem.Equals ("Blue"))
           {
               lblOutput.Text = "Flashing Blue ; Clouds Due.";
           }
           else if (cmbMode.SelectedItem.Equals("Flashing") && cmbColour.SelectedItem.Equals ("Red"))
           {
               lblOutput.Text = "Flashing Red ; Snow Instead.";
           }
           else if (cmbMode.SelectedItem.Equals("Steady") && cmbColour.SelectedItem.Equals("Blue"))
           {
               lblOutput.Text = "Steady Blue ; Clear View.";
           }
           else if (cmbMode.SelectedItem.Equals("Steady") && cmbColour.SelectedItem.Equals("Red"))
           {
               lblOutput.Text = "Steady Red ; Rain Ahead.";
           }
           else
           {
               lblOutput.Text = "Broken Beacon light";

           }

Posted 15-May-13 9:10am

SwooshNeorPewPew

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Comments

Richard C Bishop 15-May-13 15:13pm

You are kidding right? Do you think we can read your mind or access your HUD?

SwooshNeorPewPew 15-May-13 15:15pm

Copy paste into Visual Studio?

SwooshNeorPewPew 15-May-13 15:16pm

I thought there was just something basic wrong that could be answered from just looking at it, since I'm fairly new at this

Richard C Bishop 15-May-13 15:18pm

So how do you suppose we tell you what the issue is if you do not supply the error message or even describe a problem?

SwooshNeorPewPew 15-May-13 15:21pm

Again I thought it was just something basic that was wrong, error happens when i have no item selected in Application, I just want it to display the else lblOutput.Text, gives me "NullReferanceException was unhandled"

Richard C Bishop 15-May-13 15:23pm

Still not enough information, but I found your issue anyway. You need to change the way you are checking the combobox's selected value. See my solution below.

Richard C Bishop 15-May-13 15:32pm

No problem. Did that fix your problem? Seen my updated solution?

3 solutions

Solution 1

Change your if statements to something like this:

if(cmbMode.SelectedValue.ToString() == "Flashing" && cmbColour.SelectedValue.ToString() == "Blue")

Posted 15-May-13 9:25am

Richard C Bishop

Updated 15-May-13 9:31am

v3

Comments

Sergey Alexandrovich Kryukov 15-May-13 16:15pm

Formally, this is an answer, but... this is nothing good in it, honestly. Why helping to write such trash?..
Please see my answer to see what I mean.
—SA

Richard C Bishop 15-May-13 16:19pm

I see your point. I do not understand the example you are suggesting though, can you provide a link to a resource that could help explain it? Thank you.

Sergey Alexandrovich Kryukov 15-May-13 16:21pm

There is no a resource. This is elementary. However, I had a formatting bug I fixed, and then I added a paragraphs to explain further.
Please see. Better now?
—SA

Richard C Bishop 15-May-13 16:30pm

Yes, thank you. I will study enums and begin to use them when appropriate.

Sergey Alexandrovich Kryukov 15-May-13 16:42pm

I though you know enough about them. I though so looking at your comments which are usually very reasonable, showing experience, some wisdom.
—SA

Richard C Bishop 15-May-13 16:49pm

Well I have heard of it but just never really studied it much. After going over it the last few minutes, I understand how to use it. I am still trying to understand why this is a better way (of course one reason is because it is OOP), but as far as the benefit I am unsure.

Sergey Alexandrovich Kryukov 15-May-13 17:05pm

I have a whole cycle of 3 articles on CodeProject on this topic, the third one is even very popular, and the first one is quite surprising... want to see?..
—SA

Richard C Bishop 15-May-13 17:18pm

Yes, I will navigate to them through your profile, thank you.

Sergey Alexandrovich Kryukov 15-May-13 17:24pm

You won't have a problem to find it, I only have 5 complete articles at the moment... :-)
—SA

Richard C Bishop 15-May-13 17:26pm

That is 5 more than myself, so kudos to you. Granted I have only been developing for two years.

Sergey Alexandrovich Kryukov 15-May-13 17:36pm

I got some impression of your reasonably good level, which is very good for two years of experience.
—SA

Richard C Bishop 15-May-13 17:43pm

Thank you very much. I plan to be as knowledgeable as you, OriginalGriff, and Sandeep Mewara one of these days.

Sergey Alexandrovich Kryukov 15-May-13 17:47pm

I cannot see why not.
Cheers,
—SA

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CPallini · Accepted Answer · 2013-05-15T09:30:00

Solution 2

if (as you state in the remarks) no item is selected then cmbMode.SelectedItem is a null reference and you are not allowed to call its methods (like for instance cmbMode.SelectedItem.Equals) you may handle such a condition putting this line as the very first statement of your btnPredict_Click method:

C#

if ( cmbMode.SelectedItem == null) return;

Posted 15-May-13 9:30am

CPallini

Comments

Sergey Alexandrovich Kryukov 15-May-13 16:18pm

Good point, my 5, but it won't save the OP from the complete disaster experienced right now.
Please see my answer where I try to address the root of the problem.
—SA

Sergey Alexandrovich Kryukov · Accepted Answer · 2013-05-15T10:14:00

The answers you received won't really help you to write good supportable code, because the idea is wrong from the very beginning. Like some other beginners, you are doing into a read dead end, which haunts many, these days: you tend to work with string representing objects and data, instead of working objects and data itself. This defeats the purpose of not just the OOP, but, in big part, programming itself.

Instead of

C#

if (cmbMode.SelectedValue.ToString() == "Flashing" && cmbColour.SelectedValue.ToString() == "Blue") //...

it should be something like

C#

enum CmbMode { Flashing, Steady, }
enum SignColor { Red, Blue, }

//...

CmbMode cmbMode = //...
SignColor color = //...

//...

bool snow = cmbMode == CmbMode.Flashing && color == SignColor.Red;

Are you getting the idea?

You may say that you get string from UI. Wrong. You should not. Let's assume this is a ListBox. Do you know that you can store any object as items, not strings? You may say that you need strings to show them properly in UI. Yes, but not by putting strings as items. Instead, create a wrapper class or structure and override System.ToString() to show some value. This is what the UI will actually show.

If you keep doing comparison of string and immediate "if" blocks like you do, forget programming; it's much better to do no programming than to do it the way you do, quite honestly.

—SA

Help with my C# Program

3 solutions

Solution 2

Solution 3

Solution 1

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