使用C＃将Excel单元格值从文本转换为数字

I am using Windows Application. In that Application i exported the DataGrid into Excel Successfully... Now the problem is , When i exported from Grid to the Excel Sheet, The cell values are having some green color mark on left top corner in the Excel Sheet... I thought that is type cast problem . How Shall i avoid that Problem.... and How to change the cell value from text to Number ...(i.e)Convert To Number....I am using Windows Application. In that Applica