After a morning, a calculator finally formed ....

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) {Tex                 Tbox1.text = "";             b = 2; } TextBox1.Text + = "7";

}

private void Btnnum8_click (object sender, EventArgs e) {if (b = = 1) {Tex                 Tbox1.text = "";             b = 2; } TextBox1.Text + = "8";

}

private void Btnnum9_click (object sender, EventArgs e) {if (b = = 1) {Tex                 Tbox1.text = "";             b = 2; } TextBox1.Text + = "9";

}

private void Btnnum4_click (object sender, EventArgs e) {if (b = = 1) {Tex                 Tbox1.text = "";             b = 2; } TextBox1.Text + = "4";

}

private void Btnnum5_click (object sender, EventArgs e) {if (b = = 1) {Tex                 Tbox1.text = "";             b = 2; } TextBox1.Text + = "5";

}

private void Btnnum6_click (object sender, EventArgs e) {if (b = = 1) {Tex                 Tbox1.text = "";             b = 2; } TextBox1.Text + = "6";

}

        private void Btnnum1_click (object sender, EventArgs e)          {            if (b = = 1)          {           TEXTB Ox1. Text = "";              b=2;     & nbsp;             }                     textbox1.text+= "1";  & nbsp;             

private void Btnnum2_click (object sender, EventArgs e) {if (b = = 1) {Tex                 Tbox1.text = "";             b = 2; } TextBox1.Text + = "2";

}

private void Btnnum3_click (object sender, EventArgs e) {if (b = = 1) {Tex                 Tbox1.text = "";             b = 2; } TextBox1.Text + = "3";

}

        private void Btnzero_click (object sender, EventArgs e)    & nbsp;    {                             if (b = = 1)                  {                     TextBox1.Text = "";                      B = 2;                }                  TextBox1.Text + = "0";                 if (c = = "/")                  {                     TextBox1.Text = "Error";                      MessageBox.Show ("Divisor cannot be zero");                }                 

}

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)          {          & nbsp;    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"; }         }     }

After a morning, a calculator finally formed ....