Explaining the "Option Explicit"

Many of you may have noticed the "Option Explicit" code written on the beginning of our programs. Some of you may know its purpose, many of you don't.

The Option Explicit is a "compiler directive" which is just a fancy name to say that this has nothing to do with the program itself (it will not become part of the program binary code) but rather will be only used during the time of compiling (the time where code will be transformed into machine code - binary numbers).

To understand why we use this directive, read the code below

public sub awarenessTest()
    
  auxiliar = 30
  auxiliar = auxiliar - 15
  auxiliar = auxiliar + 20
  auxiliar = auxiliar +8
  auxiliar = auxiliar - 3
  msgbox cstr(auxilliar)
  exit sub

end sub

Now if we asked the reader to tell me what would be the value that would appear in the message box by the end of the execution of this program, unless you skipped 2nd grade classes, I'm quite sure your answer would be "40". But that is not the correct answer. The answer is "0".

The reason why the answer is "0" is because the message box does not print the "auxiliar" variable; it, instead, prints the "auxilliar" variable (with 2 letters "L"). This is a common "typo" mistake, hard to find in the code and that causes terrible crashes in programs. This kind of typo is so common that it, alone, justifies the use of the "Option Explicit".

The "Option Explicit" tells the compiler to only accept variables that are previously declared by the programmer (using the "Dim" word). So although declaring variables may seem like a wast of time, not declaring them (together with not using the "Option Explicit") may cause us a much greater wast of time debugging our code. If, in our example, we had used the "Option Explicit" and had declared the auxiliar variable, the message box line would make the compiler prompt an error message, since the variable "auxilliar" is not defined, making our mistake clear.

Another reason for using the "Option Explicit" is making the use of variable prefix unnecessary. Let us explain: some programmers like to put the type of the variable as a prefix of the variable name. For example, if we had a variable x as an integer, its name would be, say, "intx" or "int_x". Let us show a few examples of how this is done:

Dim dbl_age as Double
Dim obj_mail as Object
dim intX as Integer

This nomenclature - which even has a name: "hungarian notation" - they say, makes the program easier to be read. We strongly disagree.

Once you have declared your variable and told its type, there is no need to put its type again on its name. It is just... redundant. So if you use the "Option Explicit", you are obliged to declare it and therefore don't have to use hungarian notation.

We strongly recommend you to always use the "Option Explicit" code on the top of every module.