Help with a simple beginners program

[knicksfan426]

I've created a program with 2 textboxes and a button. The user must enter a value in each textbox. When the button is clicked, a message box pops up showing the sum of the values entered in each textbox.

Here's the code:

Dim start As Integer
Dim endnumber As Integer
        
        start = TextBox1.Text
        endnumber = TextBox2.Text

       If start > 0 And endnumber > 0 Then
            Dim answer As Integer
            answer = start + endnumber    'Answer becomes the integer in textbox1 + the integer in textbox2
            MsgBox(answer)  'Message box pops up and displays the answer(the sum of textbox1 and textbox2)
        End If

Here's what i want to add: if both or only one of the textboxes have no value entered in them, i want a message box to pop up and say "Please enter a value." I've tried using the do while statement and also used if statements but i kept getting errors. Can anybody help me out here?

Thanks

[Siddharth Rout]

Sub aaa()
    Dim start As Integer, endnumber As Integer, answer As Integer
    If Len(Trim(TextBox1.Text)) = 0 Then
        TextBox1.SetFocus
        MsgBox "Please enter a value in 1st Text Box"
        Exit Sub
    ElseIf Len(Trim(TextBox2.Text)) = 0 Then
        TextBox2.SetFocus
        MsgBox "Please enter a value in the 2nd Text Box"
        Exit Sub
    End If
        
    start = TextBox1.Text
    endnumber = TextBox2.Text
    
    '-- This is not the best way to handle calculation
    '-- what if the user enters text in the textbox
    '-- i can give you the answer but I want you to
    '-- figure this out yourself. If you get stuck, ask
    '-- we will help you :)
    If start > 0 And endnumber > 0 Then
        answer = start + endnumber
        MsgBox (answer)
    End If
End Sub

[knicksfan426]

Thanks but it seems like everything is interfering. It's confusing to me since i just started coding not too long ago. For the lines like TextBox1.SetFocus(), it give me the error "'Set Focus is not a member of 'System.Windows.Forms.Textbox.'" I have no idea what that means.

Also, could you please explain to me what Len,Trim, and Set Focus do?

Thanks

[Siddharth Rout]

are you using vb6 or vb.net?

[Atheist]

That means that you're using VB.NET and should hang on for a bit until a moderator comes along and moves your thread to the VB.NET section

And meanwhile, turn on Option Strict by simply writing "Option Strict On" (without the quotationmarks) at the top of your code.

[knicksfan426]

That means that you're using VB.NET and should hang on for a bit until a moderator comes along and moves your thread to the VB.NET section

And meanwhile, turn on Option Strict by simply writing "Option Strict On" (without the quotationmarks) at the top of your code.

Thanks, what would the strict option do?

[Atheist]

You can read about option strict here. Basically its good practise to always have option strict enabled, as it, among other things, minimises the chances of unexpected program behaviour.

[knicksfan426]

Thanks dude. Do any of you guys know of any good practice programs/codes to make for a beginner like me in VB .NET? I've looked around but wasn't really able to find anything good. I'd appreciate it if someone could find me some or suggest some.

Could someone also explain to me the purpose of the "For" loop? I have the basic idea of it but I dont really see why anyone would wanna use it.

[ungas023]

i use for loop if i am to deal with numbers (integers), you should probably read the whole book first, miscrosoft got a book on vb.net, you should try it out..... goodluck...

[si_the_geek]

Thread moved from 'VB6 and Earlier' forum to 'VB.Net' (VB2002 and later) forum

[MaximilianMayrhofer]

Since you are doing this in .Net, not vb6, koolsid's code should be modified as such:

Private Sub aaa()
    Dim start, endnumber, answer As Integer
    
    Select Case True
        Case TextBox1.Text.Length = 0
            MessageBox.Show("Please enter a number in the first textbox.")
            Exit Select
        Case TextBox2.Text.Length = 0
            MessageBox.Show("Please enter a number in the second textbox.")
            Exit Select
        Case Else
            start = Integer.Parse(TextBox1.Text)
            endnumber = Integer.Parse(TextBox2.Text)
            
            If start > 0 AndAlso endnumber > 0 Then
                MessageBox.Show((start + endnumber).ToString())
            End If
            Exit Select
    End Select
End Sub

[knicksfan426]

Since you are doing this in .Net, not vb6, koolsid's code should be modified as such:

Private Sub aaa()
    Dim start, endnumber, answer As Integer
    
    Select Case True
        Case TextBox1.Text.Length = 0
            MessageBox.Show("Please enter a number in the first textbox.")
            Exit Select
        Case TextBox2.Text.Length = 0
            MessageBox.Show("Please enter a number in the second textbox.")
            Exit Select
        Case Else
            start = Integer.Parse(TextBox1.Text)
            endnumber = Integer.Parse(TextBox2.Text)
            
            If start > 0 AndAlso endnumber > 0 Then
                MessageBox.Show((start + endnumber).ToString())
            End If
            Exit Select
    End Select
End Sub

Hey thanks, I tried ur code it works fine.

A few questions about it : In ur "select case" statements, why do u put an "exit select" at the end of each case? What purpose does it serve? Is it necessary?

In my code I put:
start = textbox1.text
endnumber = textbox2.text

but you put

start = integer.parse(textbox1.text)
endnumber = integer.parse(textbox2.text)

What exactly does the integer.parse do, does it make any difference from mine?

What does the textbox.text.length work with?

Another thing I'm unsure about, in your "case else" statement, is the "if then" statement included within it or are they separate?

Lastly, near the end of ur code, it says: "MessageBox.Show((start + endnumber).ToString())."
What difference does the ".ToString()" part at the end make?

Thanks, i know its a lot of questions lol sorry but i'm novice.

[Atheist]

If you had tried using your original code with Option Strict On, you'd see why Maximilian is using Integer.Parse and ToString in his code. Basically it explicitly converts a variable from one type to another.

That said, I think TryParse is alot better suited to be used in this case.

There is no need to put Exit Select at the end of each case in a Select statement in VB.NET. However in C type languages it is needed to avoid falling through to the next case, so I believe thats where Max got that from.

[MaximilianMayrhofer]

Haha yea you caught me. Even when I code in VB.Net, I think in C type. So in my head I was writing a switch statement :P

And I agree that TryParse is a much better option, but I didn't want to spoonfeed him. I was hoping that his next thread would be something like "Oh crap how do I make sure i'm parsing an actual number" so he could learn a little more.

[Blakk_Majik]

Make sure you wrap a Try/Catch around your parse statements.

I'd also suggest using TryParse, instead of just Parse because you won't know what's in that textbox until it gets to your routine.

[knicksfan426]

more questions! lol

What does the textbox.text.length work with?

What if both textboxes are empty? How do i get the msgbox to display "Please enter a number in textbox1 and textbox2"?
I messed around with it a lot but it didn't work. Here's the complete code: I rewrote it a little bit, I'd appreciate it if you'd work off this code that i wrote.

Dim start As Integer, endnumber As Integer, answer As Integer

      Select Case True
            Case TextBox1.Text.Length = 0
                MessageBox.Show("Please enter a number in textbox 1.")

            Case TextBox2.Text.Length = 0
                MessageBox.Show("Please enter a number in textbox 2.")

            Case TextBox1.Text.Length = 0 And TextBox2.Text.Length = 0 ' This is where I'm trying to make the messagebox display that message if BOTH text boxes are empty
                MessageBox.Show("Please enter a number in textbox 1 and 2.")

            Case Else
                start = TextBox1.Text
                endnumber = TextBox2.Text
                answer = start + endnumber

                If start >= 0 And endnumber >= 0 Then
                    MessageBox.Show(answer)
                End If

[Blakk_Majik]

With the way your Case statement is set up, it will never reach the third statement. The only ones that will execute will be either of the first two, or the Case Else.

This is because you are already checking to make sure the first two textboxes are not empty. Therefore, you do not need to check if both are empty.

[knicksfan426]

GOT IT!

   Dim start As Integer, endnumber As Integer, answer As Integer

        Select Case True

            Case TextBox1.Text.Length = 0 And TextBox2.Text.Length = 0
                MessageBox.Show("Please enter a number in textbox 1 and 2.")

            Case TextBox1.Text.Length = 0
                MessageBox.Show("Please enter a number in textbox 1.")

            Case TextBox2.Text.Length = 0
                MessageBox.Show("Please enter a number in textbox 2.")

            Case Else
                start = TextBox1.Text
                endnumber = TextBox2.Text
                answer = start + endnumber

                If start >= 0 And endnumber >= 0 Then
                    MessageBox.Show(answer)
                End If
        End Select

All I had to do was change the order. One thing im still confused about, what does the "True" after "Select Case" mean? Does it work like an "if" statement?

Now comes my next dilemma. How do i make it recognize text? I assume it will only recognize numbers since the variables are all integers.

[MaximilianMayrhofer]

Using the select statement the way I did is just a little trick to analyse several conditional statements cleanly, rather than nesting a bunch of if/else statements.

Basically the structure of the select statement is something like this:

Select Case (someprimitivevariable)
Case (somevalue)
'Do somethin
End Select

What the program does is step down through the possible cases, and compare them. Above it will check if someprimitivevalue=somevalue. If it does, then the case has been satisfied and it will execute the requisite code. In my example, i've simply used a boolean variable with a value of true. One by one, the program evaluates the cases until it reaches the first one that is true.

[Blakk_Majik]

What do you mean make it recognize text?

Think about it, "text"box. That's all that's in a textbox. Just because you assign the text to an integer variable, that doesn't mean all the textbox will accept is an integer. However, that DOES mean the variable won't accept anything but an integer.

This is how the bottom part of your code should look:

Case Else
             Try
                'we will attempt to parse the text as integer
                start = Integer.TryParse(TextBox1.Text)
                endnumber = Integer.TryParse(TextBox2.Text)
                'if no errors are thrown because of format exceptions
                'we can continue processing
                answer = start + endnumber

                If start >= 0 And endnumber >= 0 Then
                    MessageBox.Show(answer)
                End If
         Catch formatex as FormatException
         'if the try parse failed, we will show a message
          Messagebox.Show("Please make sure you have a valid number in both  text boxes.")
          Catch ex as Exception
          'we will catch other errors here
           End Try
        End Select

Try/Catch is your friend. Sure, there is a performance hit for throwing an exception, but there is a much bigger cost for not handling an exception.

[Atheist]

TryParse does not throw an exception if the conversion fails, so you dont need the Try-Catch there. However it does return True/False depending on the success of the conversion so you should do something like this:

Dim start As Integer
Dim endnumber As Integer
Dim answer As Integer
If Integer.TryParse(TextBox1.Text, start) AndAlso Integer.TryParse(TextBox2.Text, endnumber) Then
    answer = start + endnumber

    If start >= 0 AndAlso endnumber >= 0 Then
        MessageBox.Show(Cstr(answer))
    Else
        MessageBox.Show("Both values have to be greater than or equal to 0")
    End If
Else
    MessageBox.Show("Please enter valid integers")
End If

If you write the code like this, theres no need for the Select statement.

[knicksfan426]

Correct me if im wrong, the tryparse is checking that a valid text has been entered in to the textbox1, which in our case, the text is an integer?

[Atheist]

Yes, TryParse will make sure the string passed to it represents a valid integer, and if it does not it will return false. However if it does, it will convert the string to an integer, return true, and the second argument you passed to it will contain the converted integer.

TryParse is a must to use when dealing with user input.