Rapid Application Development / Advanced Excel Development

VBA Best Practice

There is a lot of information floating around about how to get various things done in VBA, how to make the best use, or sometimes just the most use of VBA and Excel.
This section aims to add an element of Quality and Best Practices. These are just general guidelines, a professional developer will always assess the options and make the appropriate choice in their specific situation.
These suggestions are specific to Excel VBA in commercial settings, many will not translate to other technologies or other settings.

VBA Best Practice Series

High Quality Code - Variables

• Don't reuse variables for different purposes, avoid 'temp'
• Use clear data types, and control them (watch out for implicit coercion)
• Variants are often easier to work with than arrays
• Pass parameters byVal if they are not to be changed (watch for coercion)
• Explicitly use byRef in an input parameter is to be changed, but watch for signs to redesign
• Don't implicitly use the default property, be explicit (eg range.value)
• Magic numbers and strings should be made into constants.
• Use explicit data casting Cstr() Cbool() etc
• Code with early binding if at all possible (new), change to late binding to support multiple versions or if component may not be installed. Late can be slower and may need better error handling.
• Can define all variables together at top or just before they are needed both have pros and cons.
• Sometimes a simple i, j, x or y is better than a long datatype prefixed descriptive name for a loop index
• Boolean variable should be named so True or False make sense - eg use done rather than status
• Booleans should be positive eg if not found then. rather than if not notFound then.
• Never mess with a loop counter within the loop.