Private Declare Function SendMessage Lib "user32.dll" Alias "SendMessageA" (ByVal hwnd As Long, ByVal wMsg As Long, ByVal wParam As Long, lParam As Any) As Long
Private Declare Function FindWindow Lib "user32.dll" Alias "FindWindowA" (ByVal lpClassName As String, ByVal lpWindowName As String) As Long
Private Declare Function FindWindowEx Lib "user32" Alias "FindWindowExA" (ByVal hWnd1 As Long, ByVal hWnd2 As Long, ByVal lpsz1 As String, ByVal lpsz2 As String) As Long

Function sqrx(ByVal x As Double) As String '计算平方根（比VB DOUBLE 类型精度高）
Dim temp As String, i As Long, j As Long
Shell "Calc.EXE", vbMinimizedNoFocus '运行计算器
temp = x & "y0.5="
For i = 1 To Len(temp)
SendKeys Mid(temp, i, 1), True '向计算器顺序发送按键消息X (X^Y) 0.5=
Next
temp = String(64, Chr(0))
i = FindWindow(vbNullString, "计算器") '窗口句柄
j = FindWindowEx(i, ByVal 0&, "Edit", vbNullString) '编辑框句柄
SendMessage j, &HD, Len(temp), ByVal temp '发送编辑框文本至temp
SendKeys "%{F4}", True '调用ALT+F4关闭计算器窗口
sqrx = temp
End Function

Private Sub Command1_Click()
Dim i As Integer
For i = 17 To 24
Debug.Print "sqrx(" & i & ")=" & sqrx(i)
Next
End Sub

返回：
sqrx(17)=4.1231056256176605498214098559741                              
sqrx(18)=4.2426406871192851464050661726291                              
sqrx(19)=4.3588989435406735522369819838596                              
sqrx(20)=4.4721359549995793928183473374626                              
sqrx(21)=4.582575694955840006588047193728                               
sqrx(22)=4.6904157598234295545656301135445                              
sqrx(23)=4.7958315233127195415974380641627                              
sqrx(24)=4.8989794855663561963945681494118