Creating user-defined Excel functions (UDFs) – Temperature Conversion and BMI Calculation functions from scratch.
Our last two posts focused on using, or working with somebody else’s VBA code. This article will focus on creating UDF functions from scratch. We will start with a simple temperature conversion from Celsius to Fahreheit, and vice versa. We will then calculate metric Body Mass Index (BMI), graduating to an imperial BMI calculation with 3 variables.
Since we’ve already worked with VBA code, we know some basic syntax rules for our future functions:
1. Start out with
Option Explicit statement.
Note : Option Explicit statement forces explicit declaration of our variables, and gives us an error message if we have a typo instead of performing incorrect calculations.
2. Define our function name and its parameter(s)
Function FunctionName(Parameter DataType) As DataType.
Note : VBA makes definining data types optional, but it is a good habit to have.
3. Perform our calculations:
Your code goes here.
4. Exit function and return it’s value:
Creating user-defined Excel functions (UDFs) – Part 2. Improved VBA code to spell a number in a text form.
In the previous post, we created Excel UDF, which translates a number into a text form, using Dollar/Cents as default currency type. We strictly relied on VBA code snippet, published on Microsoft’s knowledge base. While working with this code, we now realize that several enhancements to this UDF would be desirable.
First of all, when dealing with even amounts, we really don’t see a point of quite redundant“No Cents” message. Secondly, it appears that this code simply formats the amount specified, instead of rounding it. As an example $ 1,256.8789 will be spelled out as One Thousand Two Hundred Fifty Six Dollars and Eighty Seven Cents, but it really should be: One Thousand Two Hundred Fifty Six Dollars and Eighty Eight Cents. Next, we probably want to change our function name to reflect the fact it only translates dollar amounts, not any other currencies, nor non-currency amounts. This is definitely a matter of personal taste, but let’s call this function SpellNumberDollar and while at it, let’s change it’s input variable from MyNumber to Amount. Let’s then create a new universal UDF (SpellNumberCurrency), which could accept any currency type, instead of limiting ourselves to dollars. After all, we don’t have anything against Euros, do we? Finally, let’s write a true SpellNumber function, to spell out a non-currency number up to the third decimal point (thousandths), instead of current precision of two decimal points (hundredths.)
Creating user-defined Excel functions (UDFs) – Part 1. VBA code to spell a number in a text form.
One of the main reasons we use spreadsheets is to perform various computations on records present. As the most popular spreadsheet application, Excel now includes over 400 built-in functions. In fact, Excel 2013 alone brought us 53 new functions. These functions cover a wide range of various commonly used calculations as simple as SUM to add all values within your range, to much more involved PMT to calculate your monthly car loan payment.
However, quite often, we still have a need for a custom function to perform our task at hand, that’s not covered by the program. Kind folks at Microsoft let us do just that, using their programming language of choice – Visual Basic for Applications (VBA.) With VBA, we can create a custom function to perform a special calculation, this custom function is officially called a user-defined functions (UDF.) You will find that UDFs are better-suited to meeting your data needs, than using a combination of multiple built-in Excel functions. They are also much easier to adopt for users, who are not particularly Excel-savvy.
The most common misconception about Excel UDFs is that you have to learn to program in order to use them. This is not entirely true, since the Web is full of fully-functioning VBA macros that you are free to “borrow.” As an example, let’s say that we would like for Excel to spell out a number we specify. For some reason you decided that you don’t want to use your precious brain-power to perform this task. Perhaps, you need to write out a very important check to prepay your remaining mortgage principal amount. You simply cannot make any mistakes on that check, and want to rely on Excel to represent the amount of your payment in text form. A simple example would be to “translate” $ 1,357.09 into One Thousand Three Hundred Fifty Seven Dollars and Nine Cents.