Option Base 1
Private Sub Form_Click()
    Const N = 5
    Const M = 5
'    Dim  ?
    Dim i, j, t
'    Open App.Path & "\" & "datain.txt"  ?  As #1
    For i = 1 To N
        For j = 1 To M
'            ?
        Next j
    Next i
    Close #1
    Print
    Print "初始矩阵为："
    Print
    For i = 1 To N
        For j = 1 To M
            Print Tab(5 * j); Mat(i, j);
        Next j
        Print
    Next i
    For i = 1 To N
        For j = 1 To M
            t = Mat(i, 2)
            Mat(i, 2) = Mat(i, 4)
'            ?
        Next j
    Next i
    Print
    Print "交换第二列和第四列后的矩阵为："
    Print
    For i = 1 To N
        For j = 1 To M
            Print Tab(5 * j); Mat(i, j);
        Next j
        Print
    Next i
End Sub