1.只要求保留N位不四舍5入 float f = 0.55555f;

                                      int i =(int)(f * 100);

                                       f = (float)(i*1.0)/100;

2.保留N位,四舍五入 . decimal d= decimal.Round(decimal.Parse( "0.55555 "),2);

3.保留N位四舍五入 Math.Round(0.55555,2)

4,保留N位四舍五入 double dbdata = 0.55555; string str1 = dbdata.ToString( "f2 ");//fN 保留N位，四舍五入

5.保留N位四舍五入 string result = String.Format( "{0:N2} ", 0.55555);//2位

                           string result = String.Format( "{0:N3} ", 0.55555);//3位

6. 保留N位四舍五入 double s=0.55555; result=s.ToString( "#0.00 ");//点后面几个0就保留几位