Workshop 1: Thai Tax Calculator CLI

Scenario: A Thai company needs a command-line tool that calculates monthly income tax, social security, and provident fund deductions for employees. Your finance team will use this to verify payroll before the full system is built.

What You'll Build

A .NET console application that takes an employee's monthly salary and optional provident fund percentage, then outputs a formatted breakdown of all deductions and net pay.

Skills Proved

• C# basics: variables, control flow, methods
• decimal arithmetic (never use double for money)
• Console I/O and string formatting
• Error handling (invalid input, negative salary)

Requirements

1. Accept input via command-line args: dotnet run --salary 50000 [--provident-fund 5]
2. Calculate Thai progressive income tax using 2024 brackets:
   • 0 - 150,000 THB/year: 0%
   • 150,001 - 300,000: 5%
   • 300,001 - 500,000: 10%
   • 500,001 - 750,000: 15%
   • 750,001 - 1,000,000: 20%
   • 1,000,001 - 2,000,000: 25%
   • 2,000,001 - 5,000,000: 30%
   • Over 5,000,000: 35%
   • Hint: Annualize the monthly salary, calculate annual tax, divide by 12
3. Calculate social security: 5% of salary, capped at 750 THB/month (salary cap 15,000 THB)
4. Calculate provident fund: employee contribution percentage (default 0%), capped at 500,000 THB/year
5. Output a formatted breakdown:

=== Monthly Payroll Summary ===
Gross Salary:     50,000.00 THB
Income Tax:       3,541.67 THB
Social Security:    750.00 THB
Provident Fund:   2,500.00 THB (5%)
--------------------------------
Net Pay:          43,208.33 THB

6. Handle invalid input (negative salary, non-numeric args) with clear error messages and exit code 1

Stretch Goals

• Add --help flag with usage instructions
• Support annual salary input mode (--annual flag)
• Output as JSON (--format json) for integration with other tools
• Read tax brackets from appsettings.json so they can be updated without recompiling

Connection to Final Project

This calculator becomes the core tax computation engine in your Payroll & Benefits Management System. Getting the math right here — especially decimal precision — prevents expensive payroll errors in production.