怎么编控制台应用程序 使他能计算给定一元二次方程的根

能帮我编一下吗

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

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            double x1 = 0;//解1
            double x2 = 0;//解2
      
            Console.WriteLine("求 ax^2+bx+c=0 的解");
            Console.Write("请输入a的值：");
            
            double a = Convert.ToInt32(Console.ReadLine());
             Console.Write("请输入b的值：");
                double b = Convert.ToInt32(Console.ReadLine());
                Console.Write("请输入c的值：");
                double c = Convert.ToInt32(Console.ReadLine());
               double dt = b * b - 4 * a * c; //Δ的值

            if (dt < 0)
            {
                Console.WriteLine("此方程无实数解.");
            }
            else if (dt == 0)
            {
                x1 = -b / 2 * a;
                Console.WriteLine("方程的解为：x1=x2= " + x1.ToString("F"));  //保留小数点后两位
            }
            else
            {
                x1 = (-b + Math.Sqrt(dt)) / 2 * a;
                x2 = (-b - Math.Sqrt(dt)) / 2 * a;
                Console.WriteLine("方程的解为：x1= " + x1.ToString("F") + ", x2= " + x2.ToString("F"));
            }

            Console.ReadKey();
        }
    }
}
当a=0的时候无法提示错误 怎么改进