VB程序总是提示说byref 参数类型不符。什么原因啊，谢谢指点。
Public Function sqrt(a As Single) As Double
sqrt = Sqr(a)
End Function
Private Sub Command1_Click()
Dim a As Integer, b As Integer, c As Integer, D As Integer
Dim X As Single, X1 As Single, X2 As Single
a = Val(InputBox("请输入a的值！"))
b = Val(InputBox("请输入b的值！"))
c = Val(InputBox("请输入c的值！"))
D = b * b - 4 * a * c
If D < 0 Then
Print "此方程无解！"
Else
If D = 0 Then
X = -b / (2 * a)
Print "此方程有相等的实数解，解为" & Str(X)
Else
X1 = (-b + sqrt(D)) / (2 * a)
X2 = (-b - sqrt(D)) / (2 * a)
Print "此方程有不同的实数解，解为" & "X1=" & X1&; "X2=" & X2



End Sub

我刚发现这个代码里掉了两个END IF ，可是加上去了还是不行。同样的错误提示。在线等！谢谢！

sqrt(byval a As Single) As Double

当不用变量D，直接把B的平方减4AC代到X1X2值里面去后，就一切正常了。这是为什么呢？请教各位大侠

楼上你好喔，这句是为了用SQRT函数的，这个定义是什么意思呢，呵呵，我也不明白

'红色部分为修改部分
Public Function sqrt(a As Single) As Double
sqrt = Sqr(a)
End Function
Private Sub Command1_Click()
Dim a As Integer, b As Integer, c As Integer, D As Single
Dim X As Single, X1 As Single, X2 As Single
a = Val(InputBox("请输入a的值！"))
b = Val(InputBox("请输入b的值！"))
c = Val(InputBox("请输入c的值！"))
D = b * b - 4 * a * c
If D < 0 Then
  Print "此方程无解！"
Else
  If D = 0 Then
    X = -b / (2 * a)
    Print "此方程有相等的实数解，解为" & Str(X)
  Else
    X1 = (-b + sqrt(D)) / (2 * a)
    X2 = (-b - sqrt(D)) / (2 * a)
    Print "此方程有不同的实数解，解为" & "X1=" & X1; "X2=" & X2
  End If
End If

End Sub