Question

What’s the main problem if I don’t declare the type of a variable? Like, Dim var1 versus Dim var1 as Integer.

Answer 1

The main reason to declare variable types in languages which allow you to use variant types is as a check on yourself. If you have a variable that you’re using to hold a string, and then by accident you pass it to a function that expects an integer, the compiler can’t tell you that you messed up unless you told it that that variable was supposed to always be a string. Instead, you’re stuck with your string being reinterpreted as an integer, which is pretty much never going to give you what you want and the results will likely be confusing, and it will be hard to track down the bug.

In pretty much all languages there are a lot of constructs where you could leave it out and your program would work, but exist as a check on the programmer. The first job of a compiler is to make your code into an executable. But the second job of the compiler is to try as much as possible to make sure that the programmer didn’t make a mistake. Especially when your program gets large, it’s easier to let the compiler find mistakes like this as opposed to trusting that you typed everything exactly right.

Additionally, there is usually some processing overhead associated with variants, but this is a more minor concern.