哪里出了问题，结果是0，求解！

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace WinFormsApp2
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        private void button1_Click(object sender, EventArgs e)
        {
            double a = Convert.ToDouble(textBox1.Text);
            double b = Convert.ToDouble(textBox3.Text);
            string v = comboBox1.SelectedItem.ToString();
            int x = 0;
            int.TryParse(v, out x);
            //x = Convert.ToInt32(v);异常
            double sum = 0.0;
            switch (x)
            {
                case '+':
                    sum = a + b;
                    break;
                case '-':
                    sum = a - b;
                    break;
                case '*':
                    sum = a * b;
                    break;
                case '/':
                    if (b != 0)
                    {
                        sum = a / b;
                    }   
                    break;
                default:break;
                    
            }
            //double sum = a + b;
            textBox4.Text = sum.ToString();
        }
        public void My_Conbobox()
        {
            comboBox1.Items.Add("+");
            comboBox1.Items.Add("-");
            comboBox1.Items.Add("*");
            comboBox1.Items.Add("/");
        }
        private void button2_Click(object sender, EventArgs e)
        {
            textBox1.Text = ""; 
            textBox3.Text = "";
            textBox4.Text = "";
           /* Application.Exit();*/
        }
        private void Form1_Load(object sender, EventArgs e)
        {
            My_Conbobox();
        }
        private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
        {

        }
    }
}

25行，你的字符串变量v是运算操作符，结果你想把它转成整型赋值给x？，那肯定直接返回false啊，所以x不会被赋值，switch里直接break了，所以sum维持了0 

记得采纳

using System;

using System.Collections.Generic;

using System.ComponentModel;

using System.Data;

using System.Drawing;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

using System.Windows.Forms;

 

namespace WinFormsApp2

{

    public partial class Form1 : Form

    {

        public Form1()

        {

            InitializeComponent();

        }

        private void button1_Click(object sender, EventArgs e)

        {

            double a = Convert.ToDouble(textBox1.Text);

            double b = Convert.ToDouble(textBox3.Text);

            string v = comboBox1.SelectedItem.ToString();
            
            char c = char.Parse(comboBox1.Text.Trim());

            //x = Convert.ToInt32(v);异常

            double sum = 0.0;

            switch (c)

            {

                case '+':

                    sum = a + b;

                    break;

                case '-':

                    sum = a - b;

                    break;

                case '*':

                    sum = a * b;

                    break;

                case '/':

                    if (b != 0)

                    {

                        sum = a / b;

                    }   

                    break;

                default:break;

                    

            }

            //double sum = a + b;

            textBox4.Text = sum.ToString();

        }

        public void My_Conbobox()

        {

            comboBox1.Items.Add("+");

            comboBox1.Items.Add("-");

            comboBox1.Items.Add("*");

            comboBox1.Items.Add("/");

        }

        private void button2_Click(object sender, EventArgs e)

        {

            textBox1.Text = ""; 

            textBox3.Text = "";

            textBox4.Text = "";

           /* Application.Exit();*/

        }

        private void Form1_Load(object sender, EventArgs e)

        {

            My_Conbobox();

        }

        private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)

        {

 

        }

    }

}