自定义数字格式字符串

详见   

double value = .086;
Console.WriteLine(value.ToString("#0.##%", CultureInfo.InvariantCulture));
// Displays 8.6%      

double value = .003;
string perMilleFmt = "#0.## " + '\u2030';
Console.WriteLine(value.ToString(perMilleFmt, CultureInfo.InvariantCulture));
// Displays 3.‰   

double value = 86000;
Console.WriteLine(value.ToString("0.###E+0", CultureInfo.InvariantCulture));
// Displays 8.6E+4
Console.WriteLine(value.ToString("0.###E+000", CultureInfo.InvariantCulture));
// Displays 8.6E+004
Console.WriteLine(value.ToString("0.###E-000", CultureInfo.InvariantCulture));
// Displays 8.6E004

double value;
value = 123;
Console.WriteLine(value.ToString("00000"));
// Displays 00123

value = 1.2;
Console.WriteLine(value.ToString("0.00", CultureInfo.InvariantCulture));
// Displays 1.20
Console.WriteLine(value.ToString("00.00", CultureInfo.InvariantCulture));
// Displays 01.20
Console.WriteLine(value.ToString("00.00", 
                  CultureInfo.CreateSpecificCulture("da-DK")));
// Displays 01,20

value = .56;
Console.WriteLine(value.ToString("0.0", CultureInfo.InvariantCulture));
// Displays 0.6

value = 12345670;
Console.WriteLine(value.ToString("#,#", CultureInfo.InvariantCulture));	
// Displays 1,234,567,0      
Console.WriteLine(value.ToString("#,#", 
                  CultureInfo.CreateSpecificCulture("el-GR")));	
// Displays 1.234.567.0      

double value;
value = 1.2;
Console.WriteLine(value.ToString("#.##", CultureInfo.InvariantCulture));
// Displays 1.2

value = 123;
Console.WriteLine(value.ToString("#####"));
// Displays 123

value = 123456;
Console.WriteLine(value.ToString("[##-##-##]"));      
// Displays [12-34-56]

value = 12345670;
Console.WriteLine(value.ToString("#"));
// Displays 12345670
Console.WriteLine(value.ToString("(###) ###-####"));
// Displays (123) 456-70