C-Calculator

Code to build calculator using .net framework in C# 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 CalCuLaToR { public partial class Form1 : Form {

declaring variables

    string operation;
    double firstoperand;
    double secondoparand;

    public Form1()
    {
        InitializeComponent();
    }

    private void Form1_Load(object sender, EventArgs e)
    {

    }

    private void button1_Click(object sender, EventArgs e)
    {

        textBox1.Text += btn_seven.Text;
    }

    private void button3_Click(object sender, EventArgs e)
    {

        textBox1.Text += btn_one.Text;
    }

    private void button12_Click(object sender, EventArgs e)
    {
        textBox1.Text += btn_six.Text;
    }

    private void button16_Click(object sender, EventArgs e)
    {
         if (operation == "+")
        {
            secondoparand = Convert.ToDouble(textBox1.Text);
            textBox1.Text = (firstoperand + secondoparand).ToString();
          
        }
        else if (operation == "-")
        {
            secondoparand = Convert.ToDouble(textBox1.Text);
            textBox1.Text = (firstoperand - secondoparand).ToString();
        }
        else if (operation == "*")
        {
            secondoparand = Convert.ToDouble(textBox1.Text);
            textBox1.Text = (firstoperand * secondoparand).ToString();
        }
        else if (operation == "/")
        {
            if (secondoparand != 0)
            {
                secondoparand = Convert.ToDouble(textBox1.Text);
                textBox1.Text = (firstoperand / secondoparand).ToString();
          
            }
            else
            {
                textBox1.Text = "DIV/Zero!";
            }

        }
    }

    private void button8_Click(object sender, EventArgs e)
    {
        operation = "+";
        firstoperand = Convert.ToDouble(textBox1.Text);
        textBox1.Text = "";

    }

    private void button10_Click(object sender, EventArgs e)
    {
        operation = "-";
        firstoperand = Convert.ToDouble(textBox1.Text);
        textBox1.Text = "";

    }

    private void button7_Click(object sender, EventArgs e)
    {
        operation = "*";
        firstoperand = Convert.ToDouble(textBox1.Text);
        textBox1.Text = "";

    }

    private void button6_Click(object sender, EventArgs e)
    {
        operation = "/";
        firstoperand = Convert.ToDouble(textBox1.Text);
        textBox1.Text = "";

    }

    private void btn_clear_Click(object sender, EventArgs e)
    {
        textBox1.Clear();
    }

    private void textBox1_TextChanged(object sender, EventArgs e)
    {

    }

    private void btn_two_Click(object sender, EventArgs e)
    {
        textBox1.Text += btn_two.Text;
    }

    private void btn_three_Click(object sender, EventArgs e)
    {
        textBox1.Text += btn_three.Text;
    }

    private void btn_four_Click(object sender, EventArgs e)
    {
        textBox1.Text += btn_four.Text;
    }

    private void btn_5_Click(object sender, EventArgs e)
    {
        textBox1.Text += btn_5.Text;
    }

    private void btn_8_Click(object sender, EventArgs e)
    {
        textBox1.Text += btn_8.Text;
    }

    private void btn_nine_Click(object sender, EventArgs e)
    {
        textBox1.Text += btn_nine.Text;
    }

    private void btn_zero_Click(object sender, EventArgs e)
    {
        textBox1.Text += btn_zero.Text;
    }
}

}