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The next lines of code we set up an array and assign
it to a variable "myString".
For i = 0 To 249 'Run this routine 250 times
myString = myArray(i)
Next, we check our variable "myString" to
see if any of the text is starts with an Alpha character. This is done
by checking our variable "myString" is equal or greater than
(=>) an "A" [ Chr(65) ] AND equal or less than (<=) a
"Z" [ Chr(90) ]. If "myString" contains an Alpha character,
it is added (cboFrom.AddItem) to the combo boxes (cboFrom, cboTo). The
idea behind this is to add all the countries to be displayed in the combo
boxes.
e.g. Australia Dollar, US Dollar, Austrian Shilling
etc.
If "myString" is equal or greater than "0"
[ Chr(48) ] but less or equal to a "9" [ chr(57) ] then this
number is added (cboCurrency.AddItem) to our cboCurrency combo box. This
combo box is used to perform our currency conversions, and is invisible
at run-time.
e.g. 1.0 , 0.5223, 0.06211 etc.
If myString >= Chr(65) And myString <= Chr(90)
Then
cboFrom.AddItem myString
cboTo.AddItem myString
ElseIf myString >= Chr(48) And myString <= Chr(57) Then
cboCurrency.AddItem myString
End If
Next
The last part of our code for the Form_Load Event
is as follows:
File1.Close
This simply closes our open file (Currency.txt)
lblFileDate.Caption = cboFrom.List(0)
The above line simply displays the date on the screen
of when the last "Currency.txt" file was updated. This enables
the user to see how current the exchange rates are at the time on entry.
"Current as of 30/11/2000"
The next two lines simply delete the first
entry in the text file out of the combo boxes.
cboFrom.RemoveItem (0)
cboTo.RemoveItem (0)
Lastly, the next four lines display the default
country in our combo boxes at start up.
cboFrom = "US Dollar"
cboTo = "Australian Dollar"
cboFrom.ListIndex = 0
CboTo.ListIndex = 1
Creating a re-usable Function
Private Function CalculateRate()
Dim a, b, c, d
If TxtFrom.Text = "" Then TxtFrom.Text = 1
a = cboFrom.ListIndex
b = cboTo.ListIndex
c = cboCurrency.List(b)
d = cboCurrency.List(a)
lblTo.Caption = CCur(txtFrom.Text * c / d)
End Function
Instead of typing the same code two or three times throughout our
program, we will create a "Function" with this code in it, and call it several
times throughout our program.
The second and third lines get the INDEX value and assign it to our variable/s
(a,b). This will be used as a look-up type table.
a = cboFrom.ListIndex
b = cboTo.ListIndex
The third and fourth lines assign the text values that are found
using these listindex values, to variables c and d.
c = cboCurrency.List(b)
d = cboCurrency.List(a)
The last line of this function is where everything
all ties together to perform the currency conversion calculation.
lblTo.Caption = CCur(txtFrom.Text * c / d)
The "CCur" statement converts our number
value into a currency value, it then take the value inputted by the user
in the "txtFrom" text box and performs the calculation based
on the numbers assigned to our variables "c" and "d".
Performing the calculation on-the-fly
Private Sub txtFrom_Change()
If txtFrom.Text = "" Then
lblTo.Caption = ""
Else
CalculateRate 'Run the function if a value is inputted
End If
End Sub
In order for the calculation to take place immediately
upon the user inputting a number, we use the "Change" event
on our "txtFrom" box.
We use an If..then..Else routine to determine if the
user has typed in a number into the "txtFrom" text box. As soon
as the "txtFrom" has changed its current value, it will run
the function we created earlier (CalculateRate). If no change
(or no user input) then our function does not get run, so nothing
happens (this would occur at start up).
Private Sub cboFrom_Click()
CalculateRate
End Sub
Private Sub cboTo_Click()
CalculateRate
End Sub
The above two events are assigned to each combo
box (cboFrom & cboTo). I have made use of our "CalculateRate"
function to perform the currency conversion as soon the user changes the
country selection in our combo boxes.
Conclusion
Well, l hope you enjoyed this tutorial on creating a currency
converter in eVB as much l did in writing it. Experiment around with the
form layout, l have created something simple pictured below which l
believe is pleasing to the eye.
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