can perform some operations but not all on c# calculator? -

so far, addition , subtraction work. but, multiplication , division not. because first 2 numbers put in added , them operation done. such as, if 9 * 9 + 3 should 84, 21 on calculator. because taking 9+9 + 3; sees last operator. have absolutely no idea how fix this. there helpful insight?

public partial class form1 : form {     double num2;     double num1;     string c;      public form1()     {         initializecomponent();     }      private void btn0_click(object sender, eventargs e)     {         txtbox.text = txtbox.text + btn0.text;     }      private void btn1_click(object sender, eventargs e)     {         txtbox.text = txtbox.text + btn1.text;     }      private void btn2_click(object sender, eventargs e)     {         txtbox.text = txtbox.text + btn2.text;     }      private void btn3_click(object sender, eventargs e)     {         txtbox.text = txtbox.text + btn3.text;     }      private void btn4_click(object sender, eventargs e)     {         txtbox.text = txtbox.text + btn4.text;     }      private void btn5_click(object sender, eventargs e)     {         txtbox.text = txtbox.text + btn5.text;     }      private void btn6_click(object sender, eventargs e)     {         txtbox.text = txtbox.text + btn6.text;     }      private void btn7_click(object sender, eventargs e)     {         txtbox.text = txtbox.text + btn7.text;     }      private void btn8_click(object sender, eventargs e)     {         txtbox.text = txtbox.text + btn8.text;     }      private void btn9_click(object sender, eventargs e)     {         txtbox.text = txtbox.text + btn9.text;     }      private void btndecimal_click(object sender, eventargs e)     {         if (!txtbox.text.contains('.'))             txtbox.text += '.';     }      private void btnclear_click(object sender, eventargs e)     {         txtbox.clear();     }      private void btnaddition_click(object sender, eventargs e)     {         num1 = num1 + double.parse(txtbox.text);         c = "+";         txtbox.clear();     }      private void btnsubtraction_click(object sender, eventargs e)     {         num1 = num1 + double.parse(txtbox.text);         c = "-";         txtbox.clear();     }      private void btnmultiplication_click(object sender, eventargs e)     {         num1 = num1 + double.parse(txtbox.text);         c = "*";         txtbox.clear();     }      private void btndivision_click(object sender, eventargs e)     {         num1 = num1 + double.parse(txtbox.text);         c = "/";         txtbox.clear();     }     private void btnequals_click(object sender, eventargs e)     {          double result;          num2 = double.parse(txtbox.text);          switch (c)         {             case "+":                 result = num1 + num2;                 txtbox.text = result.tostring();                 num1 = 0;                 break;             case "-":                 result = num1 - num2;                 txtbox.text = result.tostring();                 num1 = 0;                 break;             case "*":                 result = num1 * num2;                 txtbox.text = result.tostring();                 num1 = 0;                 break;             case "/":                 if (num2 != 0)             {                 result = num1 / num2;                 txtbox.text = result.tostring();             }             else             {                 txtbox.text = "you can't divide zero... sign math 100 please =)";             }             break;             default:                 result = 0;                 break;         }      } } 

}

you need previous operation before overwriting new one:

private void btnaddition_click(object sender, eventargs e) {     num2 = double.parse(txtbox.text);     num1 = calc(num1, num2, c);     c = "+";     txtbox.clear(); } 

where calc operation on "=" now.