Features:
Enable easy addition of Units and their conversion factors.
Categories for Units for easy selection - ie Length, Weight, Distance etc.

Step 1
First step is to get some unit conversion factors to put in our datafile. For a start, I am going to
use just a few units.

LB to KG - 1lb = 0.45359237 kilograms.
KG to LB - 1KG = 2.20462262 pounds.
Mile to KM - 1 Mile = 1.609344 kilometers.
KM to Mile - 1KM = 0.621371192 miles.

Ok, now that we have some conversion numbers, lets make a datafile. The datafile will CSV, and contain 3
important values - Category, Unit Name, Unit Conversion Number.

So lets get to it. Create a text file named data.txt in your projects bin/debug directory and add the details for the units as shown - I have also included the Categories so they can be updated as well.



I will be using an identifier called "Field", but you can name it anything. With the above, the "Fields" are seperated by a comma. So anything before the first comma is Field 0, then Field 1, and Field 2 - Field0,Field1,Field2.

As you can see, there are 2 categories for the Units we have, Weight and Distance. We will be using these later on to display only the units for that selected category.

Step 2
* Create a new Project, and add 2 combo boxes, 2 textboxes, 4 labels and a button.
* Change the labels to the following, Category, Convert To, Value to Convert, Result.
* Change the Name of one of the Comboboxes to cboCategory, and place next to the label "Category".
* Change the name of the other Combobox to cbConvertTo, and place next to the label "Convert To".
* Change one textbox name to txtInputVal and place next to the label "Value to Convert".
* And lastly, name the other textbox txtResult and place it next to the "Result" label.
* Give your button text to "Convert"

This is how it should look so far,


Step 3
Under Form Class Form1, add Dim UnitConvVal As Double ' Global Variable for Unit Value.

Step 4
Now to do some coding. First we are going to make a Public Sub called Dataload.



In the above code I have included "Switch" which will be used for calling DataLoad as shown down below.

Step 5
Next, we will add the following into the sub. This includes the Data Filename, as well determining the seperator in the file.



Step 6
Now we will add a Select Case for the "Switch".
Start by adding Select Case Switch.

Now we will add the first Case, which will be "LoadCategory". This is run when Form1 is loaded (application start) and fills the Category Combobox with the list of categories from the datafile.



Field(0) is the first "field" in the Datafile, the above code will go though the lines of the data file, and searches for "Category" - and if it finds it, then it adds the second field "Field(1) to cboCategory. Look at the sample datafile at the start and you will see what I mean.

Now after that, and still within the Select Case, add the next part.



This case is "LoadUnits", which is used when a category is selected. This searches the file for the selected category (Weight or Distance) and adds the Units (Field(1)) to cboConvertTo.

Now the last case, "SelectUnit" grabs the conversion value for the select unit from cboConvertTo, and sets it in "UnitConVal".



Now we close the Select Cases, and add a "Next" for the loop.



Step 7
Now we will add code to each of the comboboxe's SelectedIndexChanged property, and also for the Calculate button as follows.

Form_Load - Call the Sub DataLoad with the Switch "LoadCategory" when the form loads, and fills the combobox with the Categories.
DataLoad("LoadCategory") ' Switch to DataLoad to load Categories on form load..

cboCategory_SelectedIndexChanged - Calls the Sub DataLoad with the Switch "LoadUnits" when a Category is selected.


cboConvertTo_SelectedIndexChanged - Calls the Sub DataLoad with the Switch "SelectUnit" when a Conversion Unit is selected from cboConvertTo.
DataLoad("SelectUnit")

And btnCalculate - First checks to see if anything is entered in txtInputVal, and if there is - proceed to calculate and display the conversion, otherwise show a message box reminding to enter a value.


Step 8
Now the code that you should end up with is


Now run the program, and if all goes well - the Category combobox should be filled with all the categories (in this case - Weight and Distance). Now select a category and a list of available units should be filled in the next combobox. Next, select a unit to convert, then enter a value in the textbox and click "Convert" - and the result should if all goes well - be displayed in the Results textbox. Try this for each of the categories and units.



As you have noticed, I havn't formated the result which is why there are quite a few decimal places, but you can use something like FormatNumber(CStr(CDbl(txtInputVal.Text) * UnitConvVal), 2).

Now, try adding a new category and a conversion unit to the datafile and see if it shows up in the program.

Thanks for reading.

Screenshots (Forgot to add them when I transfered sorry).