CalculatorCli.cs

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namespace CalculatorLibrary {
 
public static class CalculatorCli {
  public const string UsageText = "Usage: CalculatorApp <add|subtract|multiply|divide> <a> <b>";
 
  public static string Run(string[] args) {
    if (args.Length != 3) {
      throw new ArgumentException($"Expected 3 arguments (operation, a, b) but got {args.Length}. {UsageText}");
    }
 
    string operation = args[0].Trim().ToLowerInvariant();
 
    if (!int.TryParse(args[1], out int a)) {
      throw new ArgumentException($"'{args[1]}' is not a valid 32-bit integer for <a>. {UsageText}");
    }
 
    if (!int.TryParse(args[2], out int b)) {
      throw new ArgumentException($"'{args[2]}' is not a valid 32-bit integer for <b>. {UsageText}");
    }
 
    var calculator = new Calculator();
 
    int result = operation switch {
      "add" => calculator.Add(a, b),
        "subtract" => calculator.Subtract(a, b),
        "multiply" => calculator.Multiply(a, b),
        "divide" => calculator.Divide(a, b),
        _ => throw new ArgumentException($"Unknown operation '{args[0]}'. {UsageText}"),
    };
 
    return $"{a} {operation} {b} = {result}";
  }
 
  public static string RunDemo() {
    var calculator = new Calculator();
    var lines = new System.Text.StringBuilder();
    lines.AppendLine("Calculator Application Running (no arguments given, showing the built-in demo)...");
    lines.AppendLine($"2 add 2 = {calculator.Add(2, 2)}");
    lines.AppendLine($"2 multiply 2 = {calculator.Multiply(2, 2)}");
    lines.AppendLine($"2 subtract 2 = {calculator.Subtract(2, 2)}");
    lines.AppendLine($"2 divide 2 = {calculator.Divide(2, 2)}");
    lines.Append(UsageText);
    return lines.ToString();
  }
}
}