vb中的基本收银机应用程序

Question

我正在尝试制作一个收银机窗口形式（看起来如下图所示），我知道我正在过度思考这个但是我对vb很新，真的很困惑。但它只需要添加和减去余额。我需要帮助找出如何在这里进行数学计算，比如因为用户将输入所有值，我们如何预测他们将在代码中输入什么？

这是我到目前为止所拥有的：

Public Class frmCashRegister

    Dim Total As Decimal
    Dim Subtract As Decimal
    Dim Balance As Decimal


    Private Sub btnAdd_Click(sender As System.Object, e As System.EventArgs) Handles btnAdd.Click
        txtBalance.Text = FormatCurrency(Val(txtAmount.Text))
    End Sub

    Private Sub txtBalance_TextChanged(sender As System.Object, e As System.EventArgs) Handles txtBalance.TextChanged
        If (txtBalance.Text < 0) Then
            MsgBox("Transaction resulted in negative balance, please try again!")
        End If
    End Sub

    Private Sub txtAmount_KeyPress(sender As System.Object, ByVal e As System.Windows.Forms.KeyPressEventArgs) Handles txtAmount.KeyPress
        If Asc(e.KeyChar) <> 8 Then
            If Asc(e.KeyChar) < 48 Or Asc(e.KeyChar) > 57 Then
                e.Handled = True
            End If
        End If
    End Sub
End Class

Answer 1

首先，您需要筛选所有输入，以确保用户无法输入任何可能导致错误的内容。在简单的收银机的情况下，您需要确保数字，减去添加和可能的输入键工作。至于你的数学，你需要在这种情况下保持一个变量与你的运行总数平衡，然后当你添加和减去你的值并用Value更新你的余额TextBox时，你将更新这个变量。这是关于如何做到这一点的想法。

Dim Total As Decimal
Dim Subtract As Decimal
Dim Balance As Decimal


Private Sub btnAdd_Click(sender As System.Object, e As System.EventArgs) Handles btnAdd.Click
    Balance += Decimal.Parse(txtAmount.Text) 'Same as  Balance = Balance + Decimal.Parse(txtAmount.Text)
    txtBalance.Text = FormatCurrency(Balance)
    txtAmount.Text = ""
End Sub


Private Sub btnSubtract_Click(sender As System.Object, e As System.EventArgs) Handles btnSubtract.Click
    Balance -= Decimal.Parse(txtAmount.Text) 'Same as  Balance = Balance - Decimal.Parse(txtAmount.Text)
    txtBalance.Text = FormatCurrency(Balance)
    txtAmount.Text = ""
End Sub

Private Sub txtAmount_KeyPress(sender As System.Object, e As System.Windows.Forms.KeyPressEventArgs) Handles txtAmount.KeyPress
    If Asc(e.KeyChar) <> 8 AndAlso Asc(e.KeyChar) <> &H2E Then
        If Asc(e.KeyChar) = &H2B OrElse Asc(e.KeyChar) = &HD Then
            e.Handled = True
            btnAdd.PerformClick()
        ElseIf Asc(e.KeyChar) = &H2D Then
            e.Handled = True
            btnSubtract.PerformClick()
        ElseIf Asc(e.KeyChar) < 48 Or Asc(e.KeyChar) > 57 Then
            e.Handled = True
        End If
    End If
End Sub