执行键盘事件方法如下：
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第一步，点击VS工具。
第二步，打开后，新建一个Windows窗体应用程序。
第三步，请看右下方Form的属性栏。
第四步，双击KeyDown。
第五步，输入提示按键代码，如图所示。
第六步，再次输入代码，设置属性KeyPreview为true。
第七步，运行程序，按下举例F5，则会弹出提示，表明已经成功获。
.net框架就是对API就行封装，做成一个个的类然后可以让你轻松调用，但是。net封装的内容，是常用的内容，有些东西用的时候，还是需要调用API函数，自己写，毕竟，微软不知道你要用什么函数，所以尽可能的满足用户大众口味而已。如果你需要用的比较复杂，还是调用API自己写类吧。
希望我的回答对您有所帮助
应该定义为double或者single，string类好像不能进行运算。我简单说一下控制台的方法，你要一次性输入和差积商，首先声明两个变量用来储存两个数，然后用算法一次性输出结果就ok。
Sub Main()
Dim FN As Single
Dim SN As Single
Dim ResultNum As Single
Console.WriteLine("请输入第一个数") : FN = Console.ReadLine
Console.WriteLine("请输入第二个数") : SN = Console.ReadLine
ResultNum = FN + SN
Console.WriteLine("它们的和: " ResultNum)
ResultNum = FN - SN
Console.WriteLine("它们的差: " ResultNum)
ResultNum = FN * SN
Console.WriteLine("它们的积: " ResultNum)
ResultNum = FN / SN
Console.WriteLine("它们的商: " ResultNum)
Console.ReadLine()
End Sub
用API keybd_event来模拟按键过程，但是Ctrl+Alt+Del不能模拟，前面已经定义了各个按键的值，需要按什么键替换成对应的值就行了，由于是模拟键盘按键，所以按键发送的对象是当前激活的窗口。
Option Explicit
'
'Virtual Keys, Standard Set
'
Private Const VK_LBUTTON = H1
Private Const VK_RBUTTON = H2
Private Const VK_CANCEL = H3
Private Const VK_MBUTTON = H4 'NOT contiguous with L RBUTTON
Private Const VK_BACK = H8
Private Const VK_TAB = H9
Private Const VK_CLEAR = HC
Private Const VK_RETURN = HD
Private Const VK_SHIFT = H10
Private Const VK_CONTROL = H11
Private Const VK_MENU = H12
Private Const VK_PAUSE = H13
Private Const VK_CAPITAL = H14
Private Const VK_KANA = H15
Private Const VK_HANGEUL = H15 'old name - should be here for compatibility
Private Const VK_HANGUL = H15
Private Const VK_JUNJA = H17
Private Const VK_FINAL = H18
Private Const VK_HANJA = H19
Private Const VK_KANJI = H19
Private Const VK_ESCAPE = H1B
Private Const VK_CONVERT = H1C
Private Const VK_NONCONVERT = H1D
Private Const VK_ACCEPT = H1E
Private Const VK_MODECHANGE = H1F
Private Const VK_SPACE = H20
Private Const VK_PRIOR = H21
Private Const VK_NEXT = H22
Private Const VK_END = H23
Private Const VK_HOME = H24
Private Const VK_LEFT = H25
Private Const VK_UP = H26
Private Const VK_RIGHT = H27
Private Const VK_DOWN = H28
Private Const VK_SELECT = H29
Private Const VK_PRINT = H2A
Private Const VK_EXECUTE = H2B
Private Const VK_SNAPSHOT = H2C
Private Const VK_INSERT = H2D
Private Const VK_DELETE = H2E
Private Const VK_HELP = H2F
'VK_0 thru VK_9 are the same as ASCII '0' thru '9' (=H30 - =H39)
'VK_A thru VK_Z are the same as ASCII 'A' thru 'Z' (=H41 - =H5A)
Private Const VK_LWIN = H5B
Private Const VK_RWIN = H5C
Private Const VK_APPS = H5D
Private Const VK_NUMPAD0 = H60
Private Const VK_NUMPAD1 = H61
Private Const VK_NUMPAD2 = H62
Private Const VK_NUMPAD3 = H63
Private Const VK_NUMPAD4 = H64
Private Const VK_NUMPAD5 = H65
Private Const VK_NUMPAD6 = H66
Private Const VK_NUMPAD7 = H67
Private Const VK_NUMPAD8 = H68
Private Const VK_NUMPAD9 = H69
Private Const VK_MULTIPLY = H6A
Private Const VK_ADD = H6B
Private Const VK_SEPARATOR = H6C
Private Const VK_SUBTRACT = H6D
Private Const VK_DECIMAL = H6E
Private Const VK_DIVIDE = H6F
Private Const VK_F1 = H70
Private Const VK_F2 = H71
Private Const VK_F3 = H72
Private Const VK_F4 = H73
Private Const VK_F5 = H74
Private Const VK_F6 = H75
Private Const VK_F7 = H76
Private Const VK_F8 = H77
Private Const VK_F9 = H78
Private Const VK_F10 = H79
Private Const VK_F11 = H7A
Private Const VK_F12 = H7B
Private Const VK_F13 = H7C
Private Const VK_F14 = H7D
Private Const VK_F15 = H7E
Private Const VK_F16 = H7F
Private Const VK_F17 = H80
Private Const VK_F18 = H81
Private Const VK_F19 = H82
Private Const VK_F20 = H83
Private Const VK_F21 = H84
Private Const VK_F22 = H85
Private Const VK_F23 = H86
Private Const VK_F24 = H87
Private Const VK_NUMLOCK = H90
Private Const VK_SCROLL = H91
'
'VK_L* VK_R* - left and right Alt, Ctrl and Shift virtual keys.
'Used only as parameters to GetAsyncKeyState() and GetKeyState().
'No other API or message will distinguish left and right keys in this way.
'
Private Const VK_LSHIFT = HA0
Private Const VK_RSHIFT = HA1
Private Const VK_LCONTROL = HA2
Private Const VK_RCONTROL = HA3
Private Const VK_LMENU = HA4
Private Const VK_RMENU = HA5
'dwFlags
Private Const KEYEVENTF_EXTENDEDKEY = H1
Private Const KEYEVENTF_KEYUP = H2
Private Declare Sub keybd_event Lib "user32" (ByVal bVk As Byte, ByVal bScan As Byte, ByVal dwFlags As Long, ByVal dwExtraInfo As Long)
Private Sub Command1_Click()
Call keybd_event(VK_MENU, 0, KEYEVENTF_EXTENDEDKEY, 0) '按下Alt键
Call keybd_event(VK_SNAPSHOT, 0, KEYEVENTF_EXTENDEDKEY, 0) '按下Print Screen键
Call keybd_event(VK_SNAPSHOT, 0, KEYEVENTF_EXTENDEDKEY Or KEYEVENTF_KEYUP, 0) '抬起Print Screen键
Call keybd_event(VK_MENU, 0, KEYEVENTF_EXTENDEDKEY Or KEYEVENTF_KEYUP, 0) '抬起Alt键
Call keybd_event(VK_LWIN, 0, KEYEVENTF_EXTENDEDKEY, 0) '按下Win键
Call keybd_event(VK_LWIN, 0, KEYEVENTF_EXTENDEDKEY Or KEYEVENTF_KEYUP, 0) '抬起Win键
Call keybd_event(VK_NUMLOCK, 0, KEYEVENTF_EXTENDEDKEY, 0) '按下Num Lock键
Call keybd_event(VK_NUMLOCK, 0, KEYEVENTF_EXTENDEDKEY Or KEYEVENTF_KEYUP, 0) '抬起Num Lock键
End Sub