为什么这个 bool 不能识别正在使用？

Question

I've made an example of typing in first and last name. Why doesn't the assigned variable "EmptyInput" recognize it's being used even though I've added a false and true value? I don't know what the green wavy line underneath is called.

using System.Collections.Generic;
using System;
using System.Threading;

namespace MyLogbook
{
    public static class Program
    {
        class PInfo
        {
            public string FirstName;
            public string LastName;
        }
        public static void Main(string[] args)
        {

        Console.WriteLine("\tWelcome to your new logbook!");
            Console.WriteLine("\tPlease enter your first and last name.\n");

            PInfo pInfo = new PInfo();
            bool EmptyInput;
            do
            {
                Console.Write("\tFirst name: ");
                pInfo.FirstName = Console.ReadLine();

                Console.Write("\tLast name: ");
                pInfo.LastName = Console.ReadLine();

                if (!string.IsNullOrEmpty(pInfo.FirstName + pInfo.LastName))
                {
                    Console.WriteLine("\n\tHi, " + pInfo.FirstName + " " + pInfo.LastName + ".\n");
                    EmptyInput = false;
                }
                else
                {
                    Console.Write("\n\tEmpty input, please try again.\n\n");
                    EmptyInput = true;
                }
            } while (string.IsNullOrEmpty(pInfo.FirstName + pInfo.LastName));
        }
    }
}

Answer 1

Maybe you mean to do this

} while (EmptyInput);

instead of

} while (string.IsNullOrEmpty(pInfo.FirstName + pInfo.LastName));

because you're just assigning value to the variable, but never using it