Question

我试图写一个简单的GPA计算器，用户从组合框（A，B，C，D，F）上的项目和课程的学分时间输入成绩，计算将输出到文本框中。但是，我一直在文本框中获得NaN结果，但我无法理解为什么。我只有一点编程经验，所以我很感激任何帮助！

    Public Class Form1

    Public points As Double, hours As Integer

    Private Sub btnRecord_Click(sender As Object, e As EventArgs) Handles btnRecord.Click

        Dim gpaPoints As Double
        Dim creditHours As Integer
        Dim grade As String

        If cmbGrades.SelectedIndex < 0 Then
            MsgBox("Please select a grade.")
            Exit Sub
        ElseIf txtHours.Text = "" Then
            MsgBox("Please enter credit hours.")
        Else
            grade = cmbGrades.SelectedItem
            creditHours = CInt(txtHours.Text)
            gpaPoints = CalcGPA(grade, creditHours)
            points += gpaPoints
            hours += creditHours
            ClearList()
        End If

    End Sub

    Public Sub ClearList()
        cmbGrades.SelectedIndex = -1
        cmbGrades.Text = "Select a grade"
        txtHours.Text = ""
    End Sub

    Public Function CalcGPA(grade As String, creditHours As Integer)

        Dim gpaPoints As Double

        Select Case (grade)
            Case "A"
                gpaPoints = 4
            Case "B"
                gpaPoints = 3
            Case "C"
                gpaPoints = 2
            Case "D"
                gpaPoints = 1
            Case Else
                gpaPoints = 0

        End Select

        Return gpaPoints

    End Function

    Private Sub btnGpa_Click(sender As Object, e As EventArgs) Handles btnGpa.Click

        Dim calcGpa As Double = points / hours

        txtGpa.Text = FormatNumber(calcGpa, 2)

    End Sub

End Class

我基本上有一个记录按钮可以正常清除列表并允许某人输入二年级，但计算按钮不起作用，我无法解决这个问题。我衷心感谢任何帮助。

Answer 1

 Private Sub btnGpa_Click(sender As Object, e As EventArgs) Handles btnGpa.Click

   'Dim calcGpa As Double = points / hours '(**did you assign values here?** if not remove this)
   dim answer as double = 0

   CalcGPA(cmbGrades.SelectedValue, txtHours.Text )
    txtGpa.Text = FormatNumber(answer, 2)

End Sub

Answer 2

作为一般经验法则，如果您正在查看NaN，您可以查看以下内容：

使用任何NaN进行计算会产生NaN
0/0分区如果有浮点数则会给出NaN。你有一个浮点除法，所以你可以在这里检查你的计算时你的值是不是零。

VB.NET - 获得NaN结果，无法弄清楚原因

2 个答案: