c# - C#—在Convert.ToInt32(...)之后，循环将不接受非数字输入

Question

当我尝试输入退出字符串xxx时，为什么会引发异常？它在循环中以的方式工作，但在循环中不与 do ...一起使用。

转换为整数后，字符串变量仅允许我使用数字字符(如-999)退出 do ...，而循环。但是我想使循环控制变量成为“quit”而不是数字之类的词。我怎样才能做到这一点？

这是我的代码。

using System;
namespace StringInputPractice
{
    class StringInputPractice
    {
        static void Main()
        {
            // Declarations

            string inValue;
            int first;
            int second;
            int sum;

            do
            {
                Console.Write("\nEnter the first number. (Type \"xxx\" to exit):   ");
                inValue = Console.ReadLine();

                first = Convert.ToInt32(inValue);   //@@@@@
                Console.Write("\nEnter the second number. (Type \"xxx\" to exit):   ");
                inValue = Console.ReadLine();
                second = int.Parse(inValue);

                sum = first + second;

                Console.WriteLine("\nThe sum of {0} and {1} is {2}.", first,
                    second, sum);

                /* Things I've tried inside do { } and that don't work */

                //inValue = "";
                //inValue = null;
                //inValue = inValue.ToString();
                //inValue = first.ToString();
                //inValue = second.ToString();
            }

            while (inValue != "xxx");   /*If you enter a non-numeric string,
                                         * an exception is thrown at
                                         * @@@@@ above.
                                         */

            Console.ReadLine();
        }
    }
}

Answer 1

试试这个:使用int.TryParse代替Convert.ToInt32

public void myfun()
        {
            string inValue;
            int first;
            int second;
            int sum;

            do
            {
                Console.Write("\nEnter the first number. (Type \"xxx\" to exit):   ");
                inValue = Console.ReadLine();

                if (int.TryParse(inValue, out first))
                {
                   // first = Convert.ToInt32(inValue);   //@@@@@
                    Console.Write("\nEnter the second number. (Type \"xxx\" to exit):   ");
                    inValue = Console.ReadLine();
                    if(int.TryParse(inValue, out second))
                    {
                   // second = int.Parse(inValue);

                    sum = first + second;

                    Console.WriteLine("\nThe sum of {0} and {1} is {2}.", first,
                        second, sum);
                    }
                }
                /* Things I've tried inside do { } and that don't work */

                //inValue = "";
                //inValue = null;
                //inValue = inValue.ToString();
                //inValue = first.ToString();
                //inValue = second.ToString();
            }

            while (inValue != "xxx");   /*If you enter a non-numeric string,
                                     * an exception is thrown at
                                     * @@@@@ above.
                                     */

            Console.ReadLine();
        }