对象不能从DBNull转换为其他类型

解决办法:
1.if (dtedit.Rows[k][i] == DBNull.Value)
                                    num = 0;
                                else
                                    num = Convert.ToInt32(dtedit.Rows[k][i]);

2.在读取数据库数据时判断.如"Select IsNull(score,0) from score" 先把为null的数据表示为0

3. public static int ParseInt(object obj)
    {
        int reInt = -1;
        if (obj != null)
            int.TryParse(obj.ToString(), out reInt);
        return reInt;
    }