15. Build a CLI Calculator with Argument Parsing
1. Hello, World!
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3. Organize Downloads Folder by File Type
4. Delete Old Log Files Automatically
5. Find Duplicate Files Using MD5 Hashing
6. Generate Comprehensive File Inventory
7. Parse Web Server Logs for Performance Metrics
8. Extract Emails, URLs, and Phone Numbers from Text
9. Track Daily and Monthly Active Users from Apache Logs
10. Generate Formatted Text Reports with Column Alignment
11. Analyze Sales Transactions and Generate Revenue Reports
12. Clean and Validate CSV Data
13. Convert JSON API Responses to CSV
14. Parse and Validate Configuration Files
15. Build a CLI Calculator with Argument Parsing
16. Parse and Display Weather Data from JSON
17. Build a Simple Inventory System with Classes
18. Generate Markdown Table from CSV Data
19. Aggregate Sales Data by Time Period
20. Recursive Directory Size Calculator with Filtering
21. Parse and Transform Server Configuration
22. Find and Replace Across Multiple Files
23. Build a Simple Template Engine
24. CSV Data Validator with Business Rules
25. Build a Multi-Format Log Analyzer

Challenge

Problem

Command-line tools are the backbone of automation and system administration. This drill teaches you to build a simple CLI calculator that parses command-line arguments, validates input, performs calculations, and provides helpful usage instructions. You'll learn ARGV parsing, input validation, error handling, and user-friendly CLI design—skills essential for building Ruby scripts, automation tools, and system utilities.

Difficulty: Beginner

Instructions

  1. Accept operation and two numbers as arguments
  2. Support basic operations: add, subtract, multiply, divide
  3. Validate:
    • Operation is one of: add, subtract, multiply, divide
    • Both numbers are valid numeric values
  4. Perform calculation and print result formatted to 2 decimal places
  5. Handle division by zero with error message
  6. Print usage instructions if operation is invalid

Files

Editable

Hints

Hint 1

Use Float(string) to convert string to float - raises ArgumentError if invalid

Hint 2

Check array.include?(value) to validate operation

Hint 3

Use case/when for multiple conditions

Hint 4

Check n2 == 0 before dividing

Hint 5

Format with printf style: '%.2f' % number rounds to 2 decimals

Hint 6

rescue ArgumentError catches invalid number conversions

Ruby 3.4

1. Add two numbers

Input: 
calculate('add', '10', '5')
Expected Output: 
Result: 15.00

2. Subtract two numbers

Input: 
calculate('subtract', '10', '5')
Expected Output: 
Result: 5.00

3. Multiply two numbers

Input: 
calculate('multiply', '10', '5')
Expected Output: 
Result: 50.00

4. Divide two numbers

Input: 
calculate('divide', '10', '5')
Expected Output: 
Result: 2.00

5. Division by zero

Input: 
calculate('divide', '10', '0')
Expected Output: 
Error: Cannot divide by zero
+ 4 hidden test cases