1.ToString()方法
double d=12345678.2334;
Console.WriteLine(d.ToString("F2")); //1234.23
Console.WriteLine(d.ToString("###,###.00")); //12,345,678.23
2.Math.Round()方法
Math.Round(3.44, 1); //Returns 3.4.
Math.Round(3.45, 1); //Returns 3.4.
Math.Round(3.46, 1); //Returns 3.5.
Math.Round(3.445, 1); //Returns 3.4.
Math.Round(3.455, 1); //Returns 3.5.
Math.Round(3.465, 1); //Returns 3.5.
Math.Round(3.450, 1); //Returns 3.4.(补0是无效的)
Math.Round(3.4452, 2); //Returns 3.45.
Math.Round(3.4552, 2); //Returns 3.46.
Math.Round(3.4652, 2); //Returns 3.47.
"四舍六入五考虑，五后非零就进一，五后皆零看奇偶，五前为偶应舍 去，五前为奇要进一"
短一点的口诀叫“四舍、六入、五凑偶”
3.double.Parse()方法
double d=1.12345;
d=double.Parse(d.ToString("0.00")); //1.12
4.输出百分号
System.Globalization.NumberFormatInfo provider = new System.Globalization.NumberFormatInfo();
provider.PercentDecimalDigits = 2;//小数点保留几位数.
provider.PercentPositivePattern = 1;//百分号出现在何处.
double result = (double)1 / 3;//一定要用double类型.
Console.WriteLine(result.ToString("P", provider)); //33.33%
或
Console.WriteLine((result*100).ToString("#0.#0")+"%");
5.String.Format()方法
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
