using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;namespace 简单计算器
{public partial class Form1 : Form{public Form1(){InitializeComponent();}private void button1_Click(object sender, EventArgs e)//加法{string str1 = textBox1.Text;//str1保存第一个文本框输入的内容string str2 = textBox2.Text;//str2保存第二个文本框输入的内容int i1, i2;if (!int.TryParse(str1, out i1))//等价于 if (!int.TryParse(str1, out i1)==false)，将第一个文本框内容字符串转换成整型数据
            {MessageBox.Show("第一个数不是合法的整数");//弹出消息对话框return;//不要忘了return,仅仅退出所在的函数
            }if (int.TryParse(str2, out i2) == false)//将第二个文本框内容字符串转换成整型数据
            {MessageBox.Show("第二个数字不是合法的整数");//弹出消息对话框return;}int i3 = i1 + i2;//进行运算textBox3.Text = Convert.ToString(i3);// 等价于textBox3 = i3.ToString();
            }private void button2_Click(object sender, EventArgs e)//单击隐藏文本框
        {textBox1.Hide();//第一个文本框隐藏textBox2.Hide();//第二个文本框隐藏textBox3.Hide();//第三个文本框隐藏
            textBox4.Hide();textBox5.Hide();textBox6.Hide();textBox7.Hide();textBox8.Hide();textBox9.Hide();textBox10.Hide();textBox11.Hide();textBox12.Hide();}private void button3_Click(object sender, EventArgs e)//单击显示文本框
        {textBox1.Show();//第一个文本框显示textBox2.Show();//第二个文本框显示textBox3.Show();//第三个文本框显示
            textBox4.Show();textBox5.Show();textBox6.Show();textBox7.Show();textBox8.Show();textBox9.Show();textBox10.Show();textBox11.Show();textBox12.Show();}private void button4_Click(object sender, EventArgs e)//减法{string str3 = textBox4.Text;string str4 = textBox5.Text;int i3, i4;if (!int.TryParse(str3,out i3)){ MessageBox.Show("第一个数不是合法的整数");return;}if (!int.TryParse(str4,out i4)) {MessageBox.Show("第二个数不是合法的数据");}int i5 = i3 -i4;textBox6.Text = Convert.ToString(i5);}private void button5_Click(object sender, EventArgs e)//乘法{string str3 = textBox7.Text;string str4 = textBox8.Text;int i3, i4;if (!int.TryParse(str3, out i3)){MessageBox.Show("第一个数不是合法的整数");return;}if (!int.TryParse(str4, out i4)){MessageBox.Show("第二个数不是合法的数据");}int i5 = i3 *i4;textBox9.Text = Convert.ToString(i5);}private void button6_Click(object sender, EventArgs e)//除法{string str3 = textBox10.Text;string str4 = textBox11.Text;int i3, i4;if (!int.TryParse(str3, out i3)){MessageBox.Show("第一个数不是合法的整数");return;}if (!int.TryParse(str4, out i4)){MessageBox.Show("第二个数不是合法的数据");}int i5 = i3 / i4;textBox12.Text = Convert.ToString(i5);}}
}

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 计算器2._0
{public partial class Form1 : Form{public Form1(){InitializeComponent();}private void button1_Click(object sender, EventArgs e){/********************************MessageBox.Show(Convert.ToString(comboBox1.SelectedIndex));//下拉序号MessageBox.Show(Convert.ToString(comboBox1.SelectedItem));//下拉内容MessageBox.Show(Convert.ToString(comboBox1.SelectedText));//数据库会用到MessageBox.Show(Convert.ToString(comboBox1.SelectedValue));//数据库会用到**********************************/string s1 = textBox1.Text;string s2 = textBox2.Text;int i1, i2;i1 = Convert.ToInt32(s1);i2 = Convert.ToInt32(s2);int result;switch (comboBox1.SelectedIndex) //多选框的序号
            {case 0:result = i1 + i2;break;case 1:result = i1 - i2;break;case 2:result = i1 * i2;break;case 3:if (i2 == 0) //检查除数是否为零
                    {MessageBox.Show("除数不能为零！！！");return;}result = i1 / i2;break;default://防患于未然throw new Exception("未知的运算符");       }textBox3.Text = Convert.ToString(result);}}
}