C# - lr1

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace lr1
{
    class Program
    {
        static void Main(string[] args)
        {
            float num1 = 0, num2 = 0, res = 0;
            string op = "";
            bool show_res;

            do
            {
                show_res = true;
                do // check if data is correct
                {
                    Console.Write("Enter 1st number: ");
                } while (!float.TryParse(Console.ReadLine(), out num1));

                do // check if data is correct
                {
                    Console.Write("Enter 2nd number: ");
                } while (!float.TryParse(Console.ReadLine(), out num2));

                Console.Write("Choose operation from {/, *, -, +}: ");
                op = Console.ReadLine();
                switch (op)
                {
                    case "+":
                        res = num1 + num2;
                        break;
                    case "-":
                        res = num1 - num2;
                        break;
                    case "*":
                        res = num1 * num2;
                        break;
                    case "/":
                        if (num2 != 0)
                            res = num1 / num2;
                        else
                        {
                            Console.WriteLine("Error: Division by zero!");
                            show_res = false;
                        }
                        break;
                    default:  // if data is incorrect
                        Console.WriteLine("Non-existent option chosen, try again!");
                        show_res = false;
                        break;
                }

                if (show_res)
                    Console.WriteLine(String.Format("{0}{1}{2} = {3}", num1, op, num2, res));

                Console.Write("\nEnter 0 to exit or nothing to continue: ");
            } while (Console.ReadLine() != "0");
        }
    }
}