1.System.Globalization.NumberFormatInfo provider = new System.Globalization.NumberFormatInfo();

provider.NumberDecimalDigits =intDecLength; //要設定的小數位數

double strCashAmt=Convert.ToDouble(this.txtCashAmt.Text); //先把控件內的值轉成double

this.txtCashAmt.Text = strCashAmt.ToString("N",provider); //再利用ToString函數格式化小數位數

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

C#下如果显示保留小数位数，及百分号的解决方法:

1、用NumberFormatInfo类来解决:

System.Globalization.NumberFormatInfo provider = new System.Globalization.NumberFormatInfo();

provider.PercentDecimalDigits = 2;//小数点保留几位数.

provider.PercentPositivePattern = 2;//百分号出现在何处.

double result = (double)1 / 3;//一定要用double类型.

Response.Write(result.ToString("P", provider));

2、用ToString()方法

 　　　　public string GetRate(double aHcount, double aTask)
        {
            string rValue; string temp = "";
            if (aTask == 0)
            {
                aTask = 1;
            } 
            double db = (aHcount / aTask) * 100;
            if (aHcount >= aTask)
            {
                rValue = "100%";
            }
            else
            {
                rValue = db.ToString("#0.#0") + "%";
            } 
            return rValue;
        } 
        string str1 = String.Format("{0:N1}", 56789); //result: 56,789.0 
        string str2 = String.Format("{0:N2}",56789); //result: 56,789.00 
        string str3 = String.Format("{0:N3}",56789); //result: 56,789.000 
        string str8 = String.Format("{0:F1}",56789); //result: 56789.0 
        string str9 = String.Format("{0:F2}",56789); //result: 56789.00 
        string str11 =(56789 / 100.0).ToString("#.##"); //result: 567.89
        string str12 = (56789 / 100).ToString("#.##"); //result: 567

C#保留小数位数