Question

我正在做计算器，如果用户没有输入num1和num2的值，我会编写代码，它会给屏幕发消息，我用if-else做了。它适用于num1和operator，但不适用于num2。我该如何解决？

If TextBox1.Text = "" Or TextBox2.Text = "" Then
            If TextBox1.Text = "" Then
                MsgBox("Please enter data to number 1 ")
                TextBox1.Focus()
                Label1.ForeColor = Color.Red
            Else
                Label1.ForeColor = SystemColors.ControlText
            End If
        ElseIf TextBox1.Text = "" Or TextBox2.Text = "" Then
            If TextBox2.Text = "" Then
                MsgBox("Please enter data to number 2")
                TextBox2.Focus()
                Label2.ForeColor = Color.Red
            Else
                Label1.ForeColor = SystemColors.ControlText
            End If
        End If

Answer 1

您的代码应该是：

If TextBox1.Text = "" Or TextBox2.Text = "" Then
    If TextBox1.Text = "" Then
        MsgBox("Please enter data to number 1 ")
        TextBox1.Focus()
        Label1.ForeColor = Color.Red
    End If
    ' Seperate the conditions because TextBox1 and TextBox2 can both be empty, so an ElseIf will not handle it
    If TextBox2.Text = "" Then
        MsgBox("Please enter data to number 2")
        TextBox2.Focus()
        Label2.ForeColor = Color.Red
    End If
Else ' Neither of them (so TextBox1 and TextBox2 won't be empty)
    Label1.ForeColor = SystemColors.ControlText
End If

当用户将TextBox1留空或TextBox2为空时，这将弹出一条消息，如果他没有留下任何两个为空，Else将启动。

有关VB.NET中条件的更多信息，请查看此处：https://www.dotnetperls.com/if-vbnet

如何在vb.net中使用嵌套的if-else

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