c# 中字符和ASCII之间的相互转换

 string mapIndex = Request.QueryString["map_index"];
            string firstIndex = mapIndex.Substring(0,1);
            string lastIndex = mapIndex.Substring(1);
            string northIndex1 = string.Empty;
            if(lastIndex == "1")
            {
                northIndex1 = lastIndex;
            }
            else
            {
                northIndex1 = Convert.ToString(Convert.ToInt32(lastIndex) - 1);
            }
            string northIndex = firstIndex + northIndex1;   //向上
            string eastIndex1 = string.Empty;
            if(firstIndex == "j")
            {
                eastIndex1 = firstIndex;
            }
            else
            {
                eastIndex1 = Convert.ToString((char)((short)Convert.ToChar(firstIndex) + 1));
            }
            string eastIndex = eastIndex1 + lastIndex;