C#小數點格式化

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.(補0是無效的)

Math.Round(3.4452, 2); //Returns 3.45.
Math.Round(3.4552, 2); //Returns 3.46.
Math.Round(3.4652, 2); //Returns 3.47.
"四捨六入五考慮，五後非零就進一，五後皆零看奇偶，五前為偶應舍 去，五前為奇要進一"
短一點的口訣叫“四舍、六入、五湊偶”

3.double.Parse()方法
double   d=1.12345;  
d=double.Parse(d.ToString("0.00"));  //1.12

4.輸出百分比符號
            System.Globalization.NumberFormatInfo provider = new System.Globalization.NumberFormatInfo();
            provider.PercentDecimalDigits = 2;//小數點保留幾位元.
            provider.PercentPositivePattern = 1;//百分比符號出現在何處.
            double result = (double)1 / 3;//一定要用double類型.
            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