不区分大小写

If TextBox2.Text = "a" AndAlso TextBox21.Text = "a" Then
        'MessageBox.Show("A")
        totCorrect = totCorrect + corAns
    ElseIf TextBox2.Text = "b" AndAlso TextBox21.Text = "b" Then
        'MessageBox.Show("B")
        totCorrect = totCorrect + corAns
    ElseIf TextBox2.Text = "c" AndAlso TextBox21.Text = "c" Then
        'MessageBox.Show("C")
        totCorrect = totCorrect + corAns
    ElseIf TextBox2.Text = "d" AndAlso TextBox21.Text = "d" Then
        'MessageBox.Show("D")
        totCorrect = totCorrect + corAns
    Else
        totWrong = totWrong + wrgAns
        Label13.Visible = True
    End If

我试图使用户输入的字母 a、b、c、d 不敏感。尝试使用UCase，但它不起作用（不确定我是否使用错误）。我在 Visual Studio 2012 中并使用 VB。任何参考文献都会很棒。

您可以使用字符串比较 http://msdn.microsoft.com/en-us/library/zkcaxw5y%28v=vs.80%29.aspx方法 ：String.Compare (String strA, String strB, Boolean ignoreCase)

Pass ignoreCase与争论true将执行不区分大小写的比较。

If String.Compare(TextBox2.Text, "a", true) = 0 AndAlso String.Compare(TextBox21.Text, "a", true) = 0 Then
        'MessageBox.Show("A")
        totCorrect = totCorrect + corAns
    ElseIf String.Compare(TextBox2.Text, "b", true) = 0 AndAlso String.Compare(TextBox21.Text, "b", true) = 0 Then
        'MessageBox.Show("B")
        totCorrect = totCorrect + corAns
    ElseIf String.Compare(TextBox2.Text, "c", true) = 0 AndAlso String.Compare(TextBox21.Text, "c", true) = 0 Then
        'MessageBox.Show("C")
        totCorrect = totCorrect + corAns
    ElseIf String.Compare(TextBox2.Text, "d", true) = 0 AndAlso String.Compare(TextBox21.Text, "d", true) = 0 Then
        'MessageBox.Show("D")
        totCorrect = totCorrect + corAns
    Else
        totWrong = totWrong + wrgAns
        Label13.Visible = True
    End If

另一个想法是使用大写或小写输入ToUpper http://msdn.microsoft.com/en-us/library/ewdd6aed.aspx or ToLower http://msdn.microsoft.com/en-us/library/e78f86at.aspx.

If TextBox2.Text.ToUpper() = "A" AndAlso TextBox21.Text.ToUpper() = "A" Then
            'MessageBox.Show("A")
            totCorrect = totCorrect + corAns
        ElseIf TextBox2.Text.ToUpper() = "B" AndAlso TextBox21.Text.ToUpper() = "B" Then
            'MessageBox.Show("B")
            totCorrect = totCorrect + corAns
        ElseIf TextBox2.Text.ToUpper() = "C" AndAlso TextBox21.Text.ToUpper() = "C" Then
            'MessageBox.Show("C")
            totCorrect = totCorrect + corAns
        ElseIf TextBox2.Text.ToUpper() = "D" AndAlso TextBox21.Text.ToUpper() = "D" Then
            'MessageBox.Show("D")
            totCorrect = totCorrect + corAns
        Else
            totWrong = totWrong + wrgAns
            Label13.Visible = True
        End If