参考答案

Private Sub C1_Click()
    Open "in5.txt" For Input As #1
    Input #1, a$
    Text1.Text = a$
    Close #1
End Sub
Private Sub C2_Click()
    a$ = Text1.Text
    b$ = ""
    n = Len(a$)
    For i = 1 To n
        b$ = b$ + UCase$(Mid$(a$, i, 1))
    Next
    Text1.Text = b$
End Sub
Private Sub C3_Click()
    Open "out5.txt" For Output As #1
    Print #1, Text1.Text
    Close #1
End Sub