Kalkulator

namespace Kalkulator
{
    public partial class Form1 : Form
    {
        Double result = 0;
        String operation = "";
        bool isOperation = false;
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {

        }

        private void textBox1_TextChanged(object sender, EventArgs e)
        {

        }

        private void button_Click(object sender, EventArgs e)
        {
            if ((textBox1.Text == "0") || (isOperation))
                textBox1.Clear();

            isOperation = false;
            Button button = (Button)sender;
            if (button.Text == ".")
            {
                if (!textBox1.Text.Contains("."))
                    textBox1.Text = textBox1.Text + button.Text;

            }
            else
                textBox1.Text = textBox1.Text + button.Text;
        }

        private void operator_Click(object sender, EventArgs e)
        {
            Button button = (Button)sender;
            if (result != 0)
            {
                button17.PerformClick();
                operation = button.Text;
                isOperation = true;
            }
            else
            {
                operation = button.Text;
                result = Double.Parse(textBox1.Text);
                isOperation = true;
            }
        }

        private void button4_Click(object sender, EventArgs e)
        {
            textBox1.Text = "0";
        }

        private void button18_Click(object sender, EventArgs e)
        {
            textBox1.Text = "0";
            result = 0;
        }

        private void button17_Click(object sender, EventArgs e)
        {
            switch (operation)
            {
                case "+":
                    textBox1.Text = (result + Double.Parse(textBox1.Text)).ToString();
                    break;
                case "-":
                    textBox1.Text = (result - Double.Parse(textBox1.Text)).ToString();
                    break;
                case "*":
                    textBox1.Text = (result * Double.Parse(textBox1.Text)).ToString();
                    break;
                case "/":
                    textBox1.Text = (result / Double.Parse(textBox1.Text)).ToString();
                    break;
                default:
                    break;
            }
            result = Double.Parse(textBox1.Text);
        }
    }
}