C# multiline calculation

问题

I'm starting on C# now. I had a problem in tackling a question my lecturer asked me to do. Below is the GUI.

http://i.share.pho.to/daa36a24_c.png

This is the code i did but i didn't manage to code part the i mentioned below

      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 WindowsFormsApplication1
       {
          public partial class Form1 : Form
          {
              public Form1()
              {
                  InitializeComponent();
              }

              private void button1_Click(object sender, EventArgs e)
              {
                  double num1;
                  double num2;
                  double answer;

                  num1 = double.Parse(textBox1.Text);
                  num2 = double.Parse(textBox2.Text);


                  textBox4.Text = Convert.ToString(answer);
              }
          }
      }

I will need to add/subtract/multiple/divide first and second number so that it will produce --> (first number + the operation + second number = the answer).

The problem is i need to select the operation by clicking on the + , - , * , / symbols on the textbox. I could do it easily by using radio button or etc but my lecturer insist on this format. Please do assist for the coding of "operation" selection. Thank you.

回答1:

You use the OnIndexChanged event of a listbox to know which operator was selected.

This will allow you to calculate on each click of the list box.

Notice in the operatorListBox1_SelectedIndexChanged event method, you use sender (the object that was clicked on) to find the SelectedItem. Cast this to a string (its an object in the listbox) and your sign will appear. (no pun intended)

using System;
using System.Windows.Forms;

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        private int firstNum = 2;
        private int secondNum = 4;
        private int answer;

        public Form2()
        {
            InitializeComponent();
            operatorListBox1.Items.Add("+");
            operatorListBox1.Items.Add("-");
            operatorListBox1.Items.Add("*");
            operatorListBox1.Items.Add("/");
            //this next line would go in your designer.cs file.  I put it here for completeness
            this.operatorListBox1.SelectedIndexChanged += new System.EventHandler(this.operatorListBox1_SelectedIndexChanged);
        }

        private void operatorListBox1_SelectedIndexChanged(object sender, EventArgs e)
        {
            calculateAnswer(((ListBox)sender).SelectedItem.ToString());
        }

        private void calculateAnswer(string sign)
        {
            switch (sign)
            {
                case "+":
                    answer = firstNum + secondNum;
                    break;
                case "-":
                    answer = firstNum - secondNum;
                    break;
                case "*":
                    answer = firstNum * secondNum;
                    break;
                case "/":
                    answer = firstNum / secondNum;
                    break;
            }
            textBox4.Text = firstNum + " " + sign + " " + secondNum + " = " + answer;
        }
    }
}

回答2:

As long as the operations are in a listBox, use this:

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 WindowsFormsApplication1
   {
      public partial class Form1 : Form
      {
          public Form1()
          {
              InitializeComponent();
          }

          private void button1_Click(object sender, EventArgs e)
          {
              double num1;
              double num2;
              double answer;
              num1 = double.Parse(textBox1.Text);
              num2 = double.Parse(textBox2.Text);
              if (listBox1.SelectedIndex == 0)
              {
              answer = num1 + num2
              }
              if (listBox1.SelectedIndex == 1)
              {
              answer = num1 - num2
              }
              if (listBox1.SelectedIndex == 2)
              {
              answer = num1 * num2
              }
              if (listBox1.SelectedIndex == 3)
              {
              answer = num1 / num2
              }
              textBox4.Text = Convert.ToString(answer);
          }
      }
  }

来源：https://stackoverflow.com/questions/19080667/c-sharp-multiline-calculation