使用vba如果表一中的a列和表二中的a列相同，则表二中的c列减表一中的c列输出到J列

可以使用 VBA 中的 For 循环和 If 语句来实现这个功能，以下是示例代码：

Sub CompareAndSubtract()
    Dim ws1 As Worksheet, ws2 As Worksheet
    Dim lastRow1 As Long, lastRow2 As Long
    Dim i As Long, j As Long
    Dim a1 As String, a2 As String
    Dim c1 As Double, c2 As Double
    
    Set ws1 = ThisWorkbook.Worksheets("表一")
    Set ws2 = ThisWorkbook.Worksheets("表二")
    lastRow1 = ws1.Cells(ws1.Rows.Count, "A").End(xlUp).Row
    lastRow2 = ws2.Cells(ws2.Rows.Count, "A").End(xlUp).Row
    
    For i = 2 To lastRow1 '从第2行开始比较
        a1 = ws1.Cells(i, "A").Value
        c1 = ws1.Cells(i, "C").Value
        
        For j = 2 To lastRow2
            a2 = ws2.Cells(j, "A").Value
            
            If a1 = a2 Then '如果两个表格的 A 列相同
                c2 = ws2.Cells(j, "C").Value
                ws2.Cells(j, "J").Value = c2 - c1 '计算并输出到 J 列
            End If
        Next j
    Next i
End Sub

请将代码中的表格名称替换为你自己的表格名称，并将代码复制到 VBA 编辑器中的模块中运行即可。