二分法求近似解 哪里错了啊

[tunney7773]

Function f(ByVal x As Single) As Double
f = x ^ 2 - 2
End Function
Private Sub Command1_Click()
Dim a As Integer, b  As Integer, m As Integer, d As Integer
a = Text1.Text
b = Text2.Text
d = Text3.Text
Do
m = (a + b) / 2
f(a) = a ^ 2 - 2
f(m) = m ^ 2 - 2
If f(a) * f(m) < 0 Then
b = m
Else
a = m
End If
Loop Until Abs(a - b) < d Or f(m) = 0
Text4.Text = "M=" & m
End Sub

[几罗星人]

首先是语法的明显错误！

'先声明了一个函数（可是你为什么后面不用他呢？）
Function f(ByVal x As Single) As Double
f = x ^ 2 - 2
End Function

Private Sub Command1_Click()
……
f(a) = a ^ 2 - 2'这两句的语法全错！！！
f(m) = m ^ 2 - 2
……

这是程序，虽然它和数学有关，但是毕竟不是数学，除了在If语句里，“=”表示相等之外，其他都是表示赋值。那么你看一下，你说前面已经声明了一个函数Function f(ByVal x As Single) As Double，那么f(a)就是表示当自变量x取到a时，函数的值。而a ^ 2 - 2也是一个数值，那么数值赋值给数值，你想干什么？ 所以，正确的代码就是把我上面列出来的这两句去掉：

f(a) = a ^ 2 - 2'不要！！
f(m) = m ^ 2 - 2

[wangyounihao]

Function f(ByVal x As Single) As Double
  f = x ^ 2 - 2
End Function


Private Sub Command1_Click()
  Dim a, b, c, d As Integer
  
  Dim aaa, bbb As Double
  a = Text1.Text
  b = Text2.Text
  d = Text3.Text
  Do
    m = (a + b) / 2
    aaa = f(a)
    bbb = f(m)
    If aaa * bbb < 0 Then
      b = m
    Else
      a = m
    End If
    Loop Until Abs(a - b) < d Or f(m) = 0
    Text4.Text = "M=" & m
End Sub

[wangyounihao]