Make a calculartor in c sharp

1. Create an new windwos forms project.
2. Design Size.
3. Add panel.
   design panel color,size,style.
4. Add button.
   calculartor button and oper button.
5. Coding button function.

Declaring variables

double fstNum,secNum;
string oper;

Identify button function

btnCE

private void btnCE_Click(object sender, EventArgs e)
        {
            textDisplay.Text = "0";
            string f, s;
            f = Convert.ToString(fstNum);
            s = Convert.ToString(secNum);

            f = "";
            s = "";

        }

backspace

private void backspace_Click(object sender, EventArgs e)
        {
            if (textDisplay.Text.Length > 0)
            {
                textDisplay.Text = textDisplay.Text.Remove(textDisplay.Text.Length - 1, 1);
            }
            if (textDisplay.Text == "")
            {
                textDisplay.Text = "0";
            
            }
        }

btn9

 private void btn9_Click(object sender, EventArgs e)
        {
            if (textDisplay.Text == "0")
            {
                textDisplay.Text = "9";

            }
            else
            {
                textDisplay.Text = textDisplay.Text + "9";
            }
        }

btnAdd

 private void btnAdd_Click(object sender, EventArgs e)
        {
           fstNum = double.Parse(textDisplay.Text);
            oper = "+";
            textDisplay.Text = "";

        }

btnPM

 private void btnPM_Click(object sender, EventArgs e)
        {
            double q = Convert.ToDouble(textDisplay.Text);
            textDisplay.Text = Convert.ToString(-1 * q);

        }

btnC

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

benDec

 private void benDec_Click(object sender, EventArgs e)
        {
            if (benDec.Text == ".")
            {
                if (!textDisplay.Text.Contains("."))
                { 
                textDisplay.Text = textDisplay.Text + benDec.Text;
                }
            
            }
        }

use switch statement out put equal

 private void btnEuq_Click(object sender, EventArgs e)
        {
            secNum = double.Parse(textDisplay.Text);
            switch (oper)
            {

                case "+":
                    textDisplay.Text = (fstNum + secNum).ToString();
                    break;
                case "-":
                    textDisplay.Text = (fstNum - secNum).ToString();
                    break;
                case "*":
                    textDisplay.Text = (fstNum * secNum).ToString();
                    break;
                case "/":
                    textDisplay.Text = (fstNum / secNum).ToString();
                    break;

                default:
                break;

            }
        }

Code download：
caluclator.zip

Reference：
https://www.youtube.com/watch?v=TYN_Pk9VKIo