http://www.cnblogs.com/furenjun/archive/2010/07/13/1776484.html
Double dValue = 95.12345;
int iValue = 10000;
string strValue = "95.12345";
string result = "";
result = Convert.ToDouble(dValue).ToString("0.00");//保留小数点后两位,结果为95.12
result = Convert.ToDouble(iValue).ToString("0.00");//10000.00
result = Convert.ToDouble(strValue).ToString("0.00");//95.12
result = Convert.ToDouble(dValue).ToString("P");//得到小数点后2位的百分比,自动 加上%号;//9512.35%
result = Convert.ToDouble(strValue).ToString("f4");//保留小数点后4位; //95.1235
//要注意的一点是 Convert.ToDouble一定要是这种双精度的,不然会报错。