User FAQs

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1) What does Strongly Typed mean ?
A programming language is strongly typed if there are no implicit type conversions.
A strongly typed programming language is one in which each data type is predefined as part of the programming language.
All constants and variables must be defined with a specific data type.
An advantage of strong data typing is that it imposes a rigorous set of rules on a programmer and therefore guarantees a certain consistency of results.

2) Is VBA a Strongly Typed programming language ?
No. Type conversions can be implicit. This has nothing to do with Option Explicit.

3) What is the difference between Value data types and Reference data types ?
A value type is also known as a primitive or simple type.
When a value data type is created, a single space in memory is allocated on the stack and is accessed directly.
Value data types are automatically given a default value of zero (or equivalent) when they are declared.
A reference type is also known as an object type.
When a reference data type is created, memory is allocated on the heap and is not accessed directly. Instead a pointer to the memory location is used.
Reference data types are automatically given a default value of Nothing when they are declared.
When you want to assign something to a reference type you must use the Set statement.

4) Can you give some examples of Value data types ?

5) Can you give some examples of Reference data types ?

6) What is a Type Declaration Character ?
It is possible to declare variables by appending a special character to the end of the variable name.

7) Can you describe the Nothing keyword in the context of reference data types ?
The Nothing value is the default value when you declare a reference data type.

It is possible to explicitly assign the Nothing value to a reference data type.
You must use the Set statement.

You can use the 'Is' keyword to test for this value

You cannot assign the Nothing value to a value data type. You will get a compile error, Object not found.

8) What are the data types of these two variables ?

The first variable (one) has type Variant.
The second variable (two) has type Integer.

9) Can you describe the Variant data type ?
The Variant is used to hold any data type, value or reference (except for fixed length strings).
It can even hold objects and user defined types.
This is the default data type if one is not specified.
The size of this data type is 16 bytes (128 bits).
The following two declarations are identical.

10) When should I use the Variant data type ?
Never use the Variant data type unless absolutely necessary.
The only situation when you should use the Variant data type is:
*) When you don't know the data type.
*) When you are writing a general helper routine that needs to work with a number of different data types.
*) When you want to pass an array of any data type into a subroutine or return an array from a function.
*) When you use the "Application.GetSaveAsFileName" method.

11) When you declare a variable as a Variant, is it a Value data type or a Reference data type ?
The Variant keyword is just a placeholder for any data type.
A Variant data type can be either a Value data type or a Reference data type.

12) Can you describe the Nothing keyword in the context of the Variant data type ?
You can explicitly assign the Nothing value to a Variant data type.
You must use the Set statement.

13) Can you describe the Variant/Decimal data type ?
The Decimal is used to store fixed point real numbers.
The Variant data type has a special sub type called Decimal.
This data type must be declared as a Variant and can only be created using the CDEC conversion function.
This can hold very large numbers and maintains precision up to 29 significant figures.
This has a binary integer value and an integer scaling factor that specifies what portion of the value is a decimal fraction.
The range is +/-79,228,162,514,264,337,593,543,950,335 (with no decimal places).
The range is +/-7.9228162514264337593543950335 (with 28 decimal places).
The size of this data type is 16 bytes (128 bits).

14) Can you identify the underlying data type of a variable ?
Yes. There are two built-in functions you can use: TYPENAME and VARTYPE.

15) Can you describe the Empty keyword ?
The Empty value is the default value when you declare a Variant data type.
The Empty value is equivalent to 0, empty string and False, in the context of value data types.

You can explicitly assign the Empty value to a Variant data type.

You can use the ISEMPTY function to test for this value.

16) Can you describe the Null keyword ?
The Null value can only be assigned explicitly to a Variant data type.
It is often used to indicate an invalid value or an error.

You can use the ISNULL function to test for this value.

17) What is the TypeOf Operator ?
This operator compares a reference data type to an actual data type and returns either True or False.

18) When would you use the Type keyword ?
This keyword can be used to define a User Defined data type.
User defined data types can contain one or more elements.
A user defined data type is a value data type.

19) Can you define a Type that contains one String and one Integer ?
When using user defined types always prefix them with the word "type_".

20) What is the difference between the following two blocks of code ?

In the first block an instance is assigned immediately using Dim As New. You have less control and you are unable to check if the object is Nothing.
In the second block an instance is created just before it is needed. You have more control and you can check if the object is Nothing.

21) What is a Collection object ?
A Collection is a built-in object that you can use to represent a group of objects.
You can refer to the members of a collection, by their key or by the position.

22) How to check if an item exists in a Collection ?
There is no simple way to check if an item exists, you just need to try and get the item and then handle the error when it is not there.
When you add the items to the collection, you will need to assign a key. This can be the same as the item (assuming it is unique).

23) What is a Dictionary object ?
Requires - Microsoft.Scripting.Runtime library.
A dictionary object can contain pairs of objects where each pair consists of an item and a unique key.
The item can be any data type (including objects).
The key can be any data type (except for arrays) although strings or numbers are typically used.
Dictionaries are often compared to associative arrays otherwise known as hash tables.
You can refer to the members of a dictionary, by their key or by the position.

24) How to check if an item exists in a Dictionary ?
You can use the Exists method passing in a particular key.

25) How to change an item in a Dictionary ?
You can only use the unique key to change a value.
A value cannot be changed using the Items collection.

26) What are the differences between a Collection and a Dictionary ?
*) When adding items the order of the arguments is different. The Collection.Add arguments are in the order Item, Key. The Dictionary.Add arguments are in the order Key, Item.
*) Unique keys are mandatory in a Dictionary but optional in a Collection.
*) Items can only be returned using the key in a Dictionary but can be returned using the key or the ordinal position (1 based) in a Collection.
*) Invalid keys will generate an error when passed to a Collection but in a Dictionary will return an empty string.
*) Unique keys are case sensitive in a Dictionary (by default, although easily changed) but are not case sensitive in a Collection (by default).
*) The Dictionary has an Exists method to test for a particular key. In a Collection you must try to retrieve the item and then handle if the key cannot be found.
*) A list of keys is available from a Dictionary using the Keys method. In a Collection you cannot get a list of the keys.

*) The items are read/write in a Dictionary but read-only in a Collection. In a Collection you cannot change a particular item you must remove and add a new item.
*) The keys are read/write in a Dictionary but read-only in a Collection.
*) You can remove all the items from a Dictionary in one go without destroying the object itself. In a Collection you can only remove one item at a time, or destroy and recreate the whole collection.
*) Both support the For-Each-Next statement for enumerating through the items. In a Dictionary you can loop through the Keys and Values. In a Collection you can loop through the Items.
*) You can add an item implicitly to a Dictionary using the Item property. In a Collection you can only use the Add method.

27) When would you use a Dictionary instead of a Collection ?
*) Retrieve keys as well as the items.
*) Accommodate changes in items and/or keys.