代码

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 WindowsFormsApplication1

{

    public partial class Form1 : Form

    {

        public Form1()

        {

            InitializeComponent();

        }

        private void textBox1_TextChanged(object sender, EventArgs e)

        {

        }

        private void button1_Click(object sender, EventArgs e)

        {

            float num1 = 0;

            float num2 = 0;

            float result = 0;

            num1 = float.Parse(textBox1.Text);  //将文本框输入的字符转换成数值

            num2 = float.Parse(textBox2.Text);

            result = num1 * num2;

            textBox3.Text = result.ToString();  //将数值转换成字符

        }

        private void button2_Click(object sender, EventArgs e)

        {

            textBox1.Text = "";

            textBox2.Text = "";

            textBox3.Text = "";

        }

    }

}

效果

QQ图片20181017224046.png