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     {         double a;         int b = 1;         string c;           public Form1()         {

            InitializeComponent();         }

        private void Form1_Load(object sender, EventArgs e)         {

        }

        private void textBox1_TextChanged(object sender, EventArgs e)         {

        }

        private void BtnNum7_Click(object sender, EventArgs e)         {             if (b == 1)             {                 textBox1.Text = "";                 b = 2;             }             textBox1.Text += "7";    

        }

        private void BtnNum8_Click(object sender, EventArgs e)         {             if (b == 1)             {                 textBox1.Text = "";                 b = 2;             }             textBox1.Text += "8";    

        }

        private void BtnNum9_Click(object sender, EventArgs e)         {             if (b == 1)             {                 textBox1.Text = "";                 b = 2;             }             textBox1.Text += "9";    

        }

        private void BtnNum4_Click(object sender, EventArgs e)         {             if (b == 1)             {                 textBox1.Text = "";                 b = 2;             }             textBox1.Text += "4";    

        }

        private void BtnNum5_Click(object sender, EventArgs e)         {             if (b == 1)             {                 textBox1.Text = "";                 b = 2;             }             textBox1.Text += "5";    

        }

        private void BtnNum6_Click(object sender, EventArgs e)         {             if (b == 1)             {                 textBox1.Text = "";                 b = 2;             }             textBox1.Text += "6";    

        }

        private void BtnNum1_Click(object sender, EventArgs e)         {             if(b == 1)             {                  textBox1 .Text ="";                    b=2 ;                       }                          textBox1.Text+="1";                         }

        private void BtnNum2_Click(object sender, EventArgs e)         {             if (b == 1)             {                 textBox1.Text = "";                 b = 2;             }             textBox1.Text += "2";    

        }

        private void BtnNum3_Click(object sender, EventArgs e)         {             if (b == 1)             {                 textBox1.Text = "";                 b = 2;             }             textBox1.Text += "3";    

        }

        private void BtnZero_Click(object sender, EventArgs e)         {                             if (b == 1)                 {                     textBox1.Text = "";                     b = 2;                 }                 textBox1.Text += "0";                 if (c == "/")                 {                     textBox1.Text = "Error";                     MessageBox.Show("除数不能为零");                 }                

        }

        private void BtnAdd_Click(object sender, EventArgs e)         {             b = 1;             a = double.Parse(textBox1.Text);             c = "+";               }

        private void BtnSub_Click(object sender, EventArgs e)         {             b = 1;             a = double.Parse(textBox1.Text);             c = "-";               }

        private void BtnMul_Click(object sender, EventArgs e)         {             b = 1;             a = double.Parse(textBox1.Text);             c = "*";            }

        private void BtnDiv_Click(object sender, EventArgs e)         {             b = 1;             a = double.Parse(textBox1.Text);             c = "/";           }

        private void BtnSqrt_Click(object sender, EventArgs e)         {             b = 1;             a = double.Parse(textBox1.Text);             c = "sqrt";              }

        private void BtnResult_Click(object sender, EventArgs e)         {             switch (c)                {                case "+": a = a + double.Parse(textBox1.Text); break;              case "-": a = a - double.Parse(textBox1.Text); break;             case "*": a = a * double.Parse(textBox1.Text); break;                case "/": a = a / double.Parse(textBox1.Text); break;                         case "sqrt": a = Math.Sqrt(a ); break;                            }                               textBox1.Text = a + "";                     b =1;         }

        private void BtnClear_Click(object sender, EventArgs e)         {             textBox1.Text = "0";          }         }     }