Visual Basic .NET

Default: current LTS .NET SDK, Option Strict On, Option Explicit On, Option Infer On, System.CommandLine for arguments, xUnit tests (tests may be written in C# or VB), Docker for a clean build.

Setup

1. dotnet new console -lang VB -n Tool and a test project; add both to a solution.
2. Set in the project file: <OptionStrict>On</OptionStrict>, <OptionExplicit>On</OptionExplicit>, <TreatWarningsAsErrors>true</TreatWarningsAsErrors>. VB has no nullable reference type analysis, so check for Nothing explicitly at boundaries.
3. Pin the SDK with global.json.

Why Option Strict matters

With Option Strict Off, VB performs late binding and implicit narrowing conversions (Dim n As Integer = "12" compiles). Errors move from compile time to run time. Turn it on for new code; when porting, turn it on file by file and fix each conversion explicitly (CInt, Integer.Parse with a culture).

Reading CSV data

• Use a real CSV parser (Microsoft.VisualBasic.FileIO.TextFieldParser handles quotes and embedded commas; or a library such as CsvHelper).
• Parse numbers and dates with CultureInfo.InvariantCulture (or the culture the file was written in) explicitly.
• Validate each row and report the line number on errors; skip-and-report beats crash-on-first-error for user-supplied files.

Comparisons people care about

For utility readings (usage and amount per month):

• Year-over-year by matching the same month of the previous year, not "12 rows ago" (months can be missing).
• Unit cost = amount / usage, with a guard for zero usage.
• Flag spikes with a simple, explainable rule (e.g. more than X % above the same month last year and above the trailing median) and print the reason with the flag.

Testing

• Keep calculations in a class library with pure functions; test them with month-boundary and missing-month cases.
• Use Decimal for money.

Verification loop

1. dotnet build with zero warnings under Option Strict On.
2. dotnet test.
3. Run against a sample CSV including a quoted field, a missing month and a zero-usage month.

Pitfalls

• Integer division: / always returns Double; use \ for integer division.
• Arrays are declared by upper bound: Dim a(3) has four elements.
• Is Nothing vs = Nothing: for value types = Nothing compares with the default value; use Is Nothing for references and .HasValue for nullable values.
• AndAlso/OrElse short-circuit; And/Or evaluate both sides.
• Legacy Microsoft.VisualBasic functions (Left, Mid, Val) still work but are 1-based and culture-dependent; prefer String methods in new code.