Is it useless to use "Dim" to declare a variable if I don't write an "as something" after it?

Question

For example, are the following two codes the same? Is it unnecessary to use Dim if I don't write for example "as integer" after that?

Sub something()

MyNumber = 10

Worksheets(1).Range("A1") = MyNumber

End Sub

and

Sub something()

Dim MyNumber

MyNumber = 10

Worksheets(1).Range("A1") = MyNumber

End Sub

Answer 1

If you Dimension a variable you are letting the compiler know that you are planning to use a certain amount of memory in advance of that variable being used. In most VBA programs on modern machines this wouldn't create a huge performance benefit, but is widely considered best practice.

One of the reasons that it is considered best practice is the auto-capitalization feature in the VBE which can help you as you're coding and debugging to spot any issues.

If you dimension a variable, and do the following:

Dim hWnd

hWnd = 1234
'// some more code....
hwnd = 2345

The VBE will automatically capitalize the w in the variable name and change it to hWnd - this can act as a small reassurance that you've got the right variable and not created a typo.

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If you don't dimension a variable, you could easily find yourself in this kind of scenario:

hWnd = 1234
'// some code here
hwnd = 2345

In this scenario, the VBE will actually change the first occurrence of hWnd to hwnd. We then go on further to create a typo of hnwd and now our code looks like this:

hwnd = 1234
'// code here
hwnd = 2345
'// code here
hnwd = 3456

And suddenly you're scrolling through lines of code trying to find out why you're getting unexpected results.

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TO BE SAFE

1. Use Option Explicit
2. Declare all variables As their respective data type or object. This also gives the added benefit of intellisense