VisualNewt Software

ARTICLE 11-DEJA-VU AGAIN

1. A Listbox
2. A Label next to the listbox labelling it "Colors"
3. An array of colors: "Red", "Orange", "Yellow", "Green", "Blue", "Indigo", "Violet"
4. A CommandButton labelled "Remove"
5. A CommandButton labelled "Add"
6. A CommandButton labelled "Find Missing"
7. A CommandButton labelled "Find Duplicates"

The program should:

1. Load the colors into the listbox
2. When the user clicks on the "Remove" button , the selected color in the listbox is removed from the list.
3. When the user clicks on the "Add" button, the selected color is added to the end (bottom) of the listbox.
4. When the user clicks on the "Find Missing" button, the program should list all the missing colors in the listbox from the master set.
5. When the user clicks on the "Find Duplicates" button, the program should list all the colors in the listbox that occur more than once.

 
Here's my take on the solution:

'-------------code starts here
'
' Article 10
'
OPTION EXPLICIT
DIM Colors(7)' our color array
'-------------- create our UI
' create a listbo
SUB CreateMyListbox
   ADDOBJECT "ListBox","MyListBox",120,10,100,120 ' leave        room for label
   ' load the colors into the listbox...assumes you've set up the array first
   MyListBox.AddItem Colors(1)
   MyListBox.AddItem Colors(2)
   MyListBox.AddItem Colors(3)
   MyListBox.AddItem Colors(4)
   MyListBox.AddItem Colors(5)
   MyListBox.AddItem Colors(6)
   MyListBox.AddItem Colors(7)
END SUB

' create a label
SUB CreateMyLabel
   ADDOBJECT "Label","MyLabel",35,5,80,20 ' to the right        of the listbox
   MyLabel.Caption = "Colors"
END SUB

' create our Remove commandbutton
SUB CreateRemoveCommandButton
   ADDOBJECT "CommandButton","Remove",10,35,100,20
   Remove.Caption = "Remove"
END SUB

' create our Add commandbutton
SUB CreateAddCommandButton
   ADDOBJECT "CommandButton","Add",10,65,100,20
   Add.Caption = "Add"
END SUB 



' create FindMissing commandbutton
SUB CreateFindMissingCommandButton
   ADDOBJECT "CommandButton","FindMissing",10,95,100,20
   FindMissing.Caption = "Find Missing"
END SUB 



' create FindDuplicates commandbutton
SUB CreateFindDuplicatesCommandButton
   ADDOBJECT "CommandButton","FindDuplicates",10,125,100,20
   FindDuplicates.Caption = "Find Duplicates"
END SUB 



'----------------event handlers
' Our Remove handler
SUB Remove_click
   ' remove the selected listbox item
   MyListBox.RemoveItem MyListBox.ListIndex
   ' MyListBox.ListIndex returns the number (array index) of the selected        item
END SUB 



' Our Add handler
SUB Add_click
   ' add the selected listbox item to the end of the listbox list
   MyListBox.AddItem MyListBox.List(MyListBox.ListIndex)
   ' MyListBox.List( ) returns the text in the list
END SUB 



' Find missing event handler
SUB FindMissing_click
   ' you probably got stuck trying to figure out how to do this... don't worry this was a trick problem.
END SUB 



' Find duplicates event handler
SUB FindDuplicates_click
   ' you probably got stuck trying to figure out how to do this... don't worry this was a trick problem.
END SUB 



'----------------main routines here
' set up our color array
SUB SETUPCOLORS
   Colors(1) = "Red"
   Colors(2) = "Orange"
   Colors(3) = "Yellow"
   Colors(4) = "Green"
   Colors(5) = "Blue"
   Colors(6) = "Indigo"
   Colors(7) = "Violet"
END SUB 



' set up our user interface
SUB SETUPUI
   CreateMyListBox
   CreateRemoveCommandButton
   CreateAddCommandButton
   CreateFindMissingCommandButton
   CreateFindDuplicatesCommandButton
END SUB 



SUB INITIALIZE
   SETUPCOLORS ' this has to be done first because its used by CreateMyListBox
   SETUPUI
END SUB 



SUB MAIN
   INITIALIZE
END SUB 



MAIN ' our normal kickstart
'-------------code ends here





Ok! I've left a couple of handlers empty because I think you would have a  hard time completing this exercise without having the benefit of this lesson.   Also, you'll notice that SETUPCOLORS and CreateMyListBox have code that's  repetitive. You load a bunch of stuff into an array or list. Wouldn't it be  nice to be able to simplify this? Well we can, and we do so using...
LOOPS    
     Your programs can not only make decisions, but they can do certain things      over and over again--sort of like deja vu. There are three basic types of  loops that you'll have to learn. One type is a "determinate" type.  This just means you always know how many times to repeat the loop. In NSBasic,  this loop is programmed using the FOR/NEXT statement. (There is also a nifty  other FOR EACH/NEXT command we'll go over next time.) 

     The syntax for a FOR/NEXT command is: 




    FOR counter = start TO end [STEP increment]
      ...your stuff....
    NEXT [counter] 
      
The loop is bracketed by the FOR and NEXT statements. And where "counter"  is a variable that keeps track of how many time you are about to go thru  the loop. "start" is the first value of "counter" when  the loop starts. The loop ends when "counter" executes the "end"th  iteration of the loop. Each time through the loop, "counter" is  incremented (or decremented) by "increment". Yup this seems confusing without an example. Here is a simple one: 



 FOR I = 1 TO 3
      MSGBOX I
 NEXT I 
 
This loop will show the MSGBOX 3 times (start = 1 end = 3) and each time  in the loop MSGBOX will show you the value of "counter". Now how  about counting from 1 to 10 but only displaying the odd numbers? Easy: 



FOR I = 1 TO 10 STEP 2
      MSGBOX I
NEXT 
Each time through the loop, the "counter" value of I will get 2 (the "increment") added to it, so the loop only executes 5 times instead of 10, and only with the odd values from 1 to 10! Cool! Also, note that we didn't specify the "counter" in the NEXT statment. NEXT instead of NEXT I. Either is fine, but explicitly stating it is better style (documentation again). 
       Now how about counting downward by 2s? 





 FOR I = 10 TO 1 STEP - 2
      MSGBOX I
 NEXT I 

 Always remember that "start" is always where you start, whether      you go up or down. Now you can also next loops (have one inside another. Try this: 

     
 FOR I = 1 TO 3
      FOR J = 1 TO 3
     	 MSGBOX "I=" & I & " J=" & J
      NEXT J
 NEXT I 



 That's all there is really to FOR statements, but they are powrerful when you know "start" and "end". But what happens when you  don't know? A good example is our last assignment.

We don't know how many colors the user deleted or how many duplicates exist. In that case, we use something known as an "indeterminate" loop. NSBasic has two types of indeterminate loops; the WHILE/WEND and the DO/LOOP.      

     The two loops are very similar, but they have two important differences. The      DO/LOOP always executes at least once, whereas the WHILE/WEND may not execute      at all. This is due to the other difference. The DO/LOOP executes at least      once because the check for whether the loop should loop is done at the end      of the loop,

     whereas the WHILE/WEND check is done at the beginning of the loop. 

     The syntax of a DO/LOOP is:      



 DO
      ...your stuff inside the loop
 LOOP [WHILE|UNTIL condition]
     
 and the WHILE/WEND      
 WHILE condition
      ...your stuff inside the loop
 WEND 
 
Let's take the example of counting from 1 to 10 again, but this time lets use indeterminate loops. 
 I = 1
 DO
      MSGBOX I
      I = I + 1
 LOOP UNTIL I = 10 
     
Note that you have to handle the "counter" and the incrementing        of the counter. It doesn't happen like in the FOR/NEXT because NSBASIC doesn't        know the start or end points. In our assignment we could do something like:      
     
 I = 1
 DO
      Colors(I) = ...
      I = I + 1
 LOOP UNTIL I = 7   


We could also write this using the other variation of the DO/LOOP: 
 I =1
 DO
      Colors(I) = ...
      I = I + 1
 LOOP WHILE I < 8 



Which one you use is really up to you, you can accomplish tasks either   way. Now the same thing using the WHILE/WEND: I = 1




WHILE I <= 7
      Colors(I) = ...
      I = I + 1
WEND 
 
Now I mentioned that DO/LOOPS always execute at least once and WHILE/WENDs  may note even execute. Here is an example: 



 I = 2
 DO
      MSGBOX I
      I = I + 1
 LOOP UNTIL I = 3
 I = 1

 WHILE I = 3
      MSGBOX I
      I = I + 1
 WEND 
     

True, this is a forced example, but it shows the point! Option Buttons Now for our widget of the day! The option button is like a checkbox. It  lets us toggle a value on and off, but unlike a checkbox, an option button  usually occurs in groups, and only one option button can be on at a time.  That is, turning one on, turns the others off. 

There is nothing new about an OptionButton. You already know all the methods,  events, properties, and how to create one! The only problem we have to deal with is the exclusive nature of the button. If you create two buttons: 



 ADDOBJECT "OptionButton","B1",10,10,100,20
 ADDOBJECT "OptionButton","B2",10,30,100,20
 ADDOBJECT "OptionButton","B3",10,50,100,20
 B1.Caption = "B1"
 B2.Caption = "B2"

 B3.Caption = "B3" 



and run it, you'll see that there is nothing inherently exclusive about the buttons! You can toggle them both on! This is a shortcoming in NSBasic,  since VisualBasic and other environments handle the exclusivitiy automatically. So what do we do? We have to write our own code to  handle option buttons. This is how: 

SUB B1_Click
      ' we know that B1 is now on, so we turn the others off...
      B2.Value = FALSE
      B3.Value = FALSE
END SUB

SUB B2_Click
      B1.Value = FALSE
      B3.Value = FALSE
END SUB

SUB B3_Click
      B1.Value = FALSE
      B2.Value = FALSE
END SUB 



That's it for option buttons really. 

     
For next time 



For next time, rewrite the colors exercise to use loops to initialize the colors and the listbox. Next time we'll go over the FOR EACH/NEXT statement  and the PictureBox widget! Stay tuned!  Cheers!