using System; using System.Collections.Generic; using System.ComponentModel; using System.Data; using System.Drawing; using System.Linq; using System.Text; using System.Windows.Forms;

namespace WindowsFormsApplication15 { public partial class Form1 : Form { public Form1() { InitializeComponent(); } double n1, n2; string type; private void button1_Click(object sender, EventArgs e) {

        Button bt = (Button)(sender);
        b1.Text = bt.Text;
        n1 = Convert.ToDouble(bt.Text);
    }

    private void button11_Click(object sender, EventArgs e)
    {
        b1.Text = "";
        type = "+";
           
    }

    private void button12_Click(object sender, EventArgs e)
    {
        b1.Text = "";
        type = "-";
           
    }

    private void button14_Click(object sender, EventArgs e)
    {
        b1.Text = "";
        type = "/";
           
    }

    private void button13_Click(object sender, EventArgs e)
    {
        b1.Text = "";
        type = "*";
           
    }

    private void button15_Click(object sender, EventArgs e)
    {
        switch (type)
        {
            case ("+"):
                n2 = Convert.ToDouble(b1.Text);
                b1.Text = Convert.ToString(n1+n2);
                break;

            case ("-"):
                n2 = Convert.ToDouble(b1.Text); 
                b1.Text = Convert.ToString(n1-n2);
                break;
            case ("*"):
                n2 = Convert.ToDouble(b1.Text); 
                b1.Text = Convert.ToString(n1*n2);
                break;
            case ("/"):
                n2 = Convert.ToDouble(b1.Text);
                b1.Text = Convert.ToString(n1/n2);
                break;
        }
       
    }

    private void back_Click(object sender, EventArgs e)
    {
        b1.Text = "";
    }

}
 

} 這是我寫的程式碼，為什麼會出現很多錯誤？