CalculatorWithTests/Program.cs

using System;

namespace Calculator
{
    internal class Program
    {
        static void Main()
        {
            Calculator calculator = new Calculator();
            while (Menu(calculator, out var operation))
            {
                int a = Argument("a");
                int b = Argument("b");
                Console.WriteLine($"Result: {operation(a, b)}");
            }
        }

        static bool Menu(Calculator calculator, out Func<int, int, float> operation)
        {
            while (true)
            {
                Console.WriteLine("Choose operation:");
                Console.WriteLine("1) Addition");
                Console.WriteLine("2) Subtraction");
                Console.WriteLine("3) Multiplication");
                Console.WriteLine("4) Division");
                Console.WriteLine("5) Power");
                Console.WriteLine("6) Exit");
                string input = Console.ReadLine();
                if (int.TryParse(input, out int result) && result >= 1 && result <= 6)
                {
                    switch (result)
                    {
                        case 1:
                            operation = calculator.Add;
                            return true;
                        case 2:
                            operation = calculator.Subtract;
                            return true;
                        case 3:
                            operation = calculator.Multiply;
                            return true;
                        case 4:
                            operation = calculator.Divide;
                            return true;
                        case 5:
                            operation = calculator.Power;
                            return true;
                        case 6:
                            operation = null;
                            return false;
                    }
                }
            }
        }

        static int Argument(string name)
        {
            while (true)
            {
                Console.Write($"Enter {name}: ");
                string input = Console.ReadLine();
                if (int.TryParse(input, out int result))
                    return result;
            }
        }
    }
}