此代码是否是此任务的正确代码？

Question

创建一个名为 swapped 的函数，它将接受两个称为 byref 的整数 (a,b) 并返回一个布尔值，如果数字已被交换，则返回 true。在例程中比较数字，如果 b>a 使用局部变量 temp 交换它们，则返回值 true，否则返回值 false。

Function swapped(ByRef a As Boolean, ByRef b As Boolean)
    a = True
    b = True
    If b > a Then
        temp = b
        b = a
        a = temp
        a = True
        b = True
    Else
        a = False
        b = False
    End If

Answer 1

首先让我们看看你的代码。

'The requirements called for 2 Integers, not Booleans.
'A Function requires a datatype, in this can a Boolean
Private Function swapped(ByRef a As Boolean, ByRef b As Boolean)
    'Assigning values here will overwrite the passed in values
    a = True
    b = True
    'What would it mean for True > True ??
    If b > a Then
        'temp isn't declared so this will not compile
        temp = b
        'here I think you are trying to do the swap
        'but all the values are True
        b = a
        a = temp
        a = True
        b = True
    Else
        a = False
        b = False

    End If
    'Function need a return value to match the datatype of the function
    'It is preceded by Return
End Function

如果您使用的是 Visual Studio（免费下载），则会为您突出显示其中的几个错误。

现在，让我们看一些可以完成任务的代码。

'Through comments you have already figured out that a and b are Integers
'In addition, Functions always need a return type. In this case a Boolean
    Function swapped(ByRef a As Integer, ByRef b As Integer) As Boolean
    'The values of a and b are passed to the function.
    'Keep the passed in value of a in a new variable
    If b > a Then
        Dim aPassedInValue = a
        'assign the value of b to a
        a = b
        'now assign the original value of a to b
        'we can't use a because we just changed the value of a in the above line
        b = aPassedInValue
        'There have been no errors so we can return True
        Return True
    Else 'We didn't swap them
        Return False
    End If
End Function

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
    Dim c As Integer = 7
    Dim d As Integer = 20
    MessageBox.Show($"c = {c}, d = {d}", "Before Swap")
    Dim ReturnValue = swapped(c, d)
    MessageBox.Show($"The return value of the swapped Function is {ReturnValue}")
    MessageBox.Show($"c = {c}, d = {d}", "After Swap")
End Sub

我认为这个练习的重点是演示 ByRef。您已更改函数中的值，并且新值反映在 Button 中的变量中。单击 Sub。

Answer 2

这是一个固定的例子。您应该将参数声明为整数而不是布尔值。函数本身应声明为布尔值

Function swapped(ByRef a As Integer, ByRef b As Integer) As Boolean

    If b > a Then
       'Declare the temp variable
        Dim temp As Integer = b

       'Change b to a
        b = a
       'Set 'a' equal to the temp variable from the original b
        a = temp

        Return True

    Else
        Return False

    End If
End Function

Public Sub test()
    Dim intA As Integer
    Dim intB As Integer
    intA = 1
    intB = 2
    'Test b>a
    'Should return True
    Dim check As Boolean
    check = swapped(intA, intB)

    'Test Not(b>a)
    'Should return False
    Dim checkfalse As Boolean
    checkfalse = swapped(2, 2)
End Sub

Answer 3

现有的两个答案都可以解决问题。这是一个没有临时变量的变量

Private Function swapped(ByRef a As Integer, ByRef b As Integer) As Boolean
    If b > a Then
        a = a + b
        b = a - b
        a = a - b
        Return True
    End If
    Return False
End Function

Sub Main()
    Dim a = 10
    Dim b = 11
    Console.WriteLine($"a: {a}, b: {b}")
    Console.WriteLine($"values were{If(swapped(a, b), " ", " not ")}swapped.")
    Console.WriteLine($"a: {a}, b: {b}")
    Console.ReadLine()
End Sub