在C＃中， Math.Round()是Math类方法，用于将值舍入到最接近的整数或小数位数。可以通过更改传递的参数的数量和类型来重载此方法。 Math.Round()方法的重载列表中共有8个方法。在这里，我们将只讨论4种方法，其余4种方法将在C＃中讨论。 Math.Round()方法|设置– 2 。
- 圆数(双)
- Math.Round(Double，Int32)
- Math.Round(十进制)
- Math.Round(Decimal，Int32)
- Math.Round(Double，Int32，MidpointRounding)
- Math.Round(Double，MidpointRounding)
- Math.Round(Decimal，Int32，MidpointRounding)
- Math.Round(十进制，MidpointRounding)
圆数(双)
此方法将双精度浮点值舍入为最接近的整数值。
句法：
public static double Round(double x)
范围：
x: A double floating-point number which is to be rounded. Type of this parameter is System.Double.
返回类型：返回最接近x的整数，返回类型为System.Double 。
注意：如果x的小数部分位于两个整数的中间，其中一个为偶数，另一个为奇数，则返回偶数。
例子：
// C# program to demonstrate the
// Math.Round(Double) method
using System;
class Geeks {
// Main method
static void Main(string[] args)
{
// Case-1
// A double value whose fractional part is
// less than the halfway between two
// consecutive integers
Double dx1 = 12.434565d;
// Output value will be 12
Console.WriteLine("Rounded value of " + dx1 +
" is " + Math.Round(dx1));
// Case-2
// A double value whose fractional part is
// greater than the halfway between two
// consecutive integers
Double dx2 = 12.634565d;
// Output value will be 13
Console.WriteLine("Rounded value of " + dx2 +
" is " + Math.Round(dx2));
}
}
Rounded value of 12.434565 is 12
Rounded value of 12.634565 is 13
说明：在上面的代码中，假设用户想要将上述指定的double值四舍五入为最接近的整数。因此，编译器将首先检查该double值是否大于或小于该double数的偶数和奇数整数值。如果小于中途值，则其输出将为下限；否则，如果大于中途值，则其输出将为上限。
Math.Round(Double，Int32)
此方法将双精度浮点值舍入为指定数量的小数位数。
句法：
public static double Round(double x, Int32 y)
范围：
x: A double floating-point number which is to be rounded. Type of this parameter is System.Double.
y: It is the number of fractional digits in the returned value. Type of this parameter is System.Int32.
返回类型：返回最接近x的整数，该整数包含与y相等的小数位数，返回类型为System.Double 。
异常：如果y的值小于0或大于15，则此方法将提供ArgumentOutOfRangeException。
例子：
// C# program to demonstrate the
// Math.Round(Double, Int32) method
using System;
class Geeks {
// Main method
static void Main(string[] args)
{
// double type
Double dx1 = 12.434565d;
// using method
Console.WriteLine("Rounded value of " + dx1 +
" is " + Math.Round(dx1, 4));
// double type
Double dx2 = 12.634565d;
// using method
Console.WriteLine("Rounded value of " + dx2 +
" is " + Math.Round(dx2,2));
}
}
Rounded value of 12.434565 is 12.4346
Rounded value of 12.634565 is 12.63
说明：方法将检查指定的十进制数字旁边的数字是否大于或等于5。如果它大于或等于5，则它将递增前一个数字，否则前一个数字将保持不变。
Math.Round(十进制)
此方法将精度为128位的十进制值四舍五入到最接近的整数值。
句法：
public static decimal Round(decimal x)
范围：
x: It is decimal number which is to be rounded. Type of this parameter is System.Decimal.
返回类型：返回最接近x的整数，返回类型为System.Decimal 。
注意：如果x的小数部分位于两个整数的中间，其中一个为偶数，另一个为奇数，则返回偶数。
例子：
// C# program to demonstrate the
// Math.Round(Decimal) method
using System;
class Geeks {
// Main method
static void Main(string[] args)
{
// Case-1
// A decimal value whose fractional part is
// less than the halfway between two
// consecutive integers
Decimal dec1 = 12.345m;
Console.WriteLine("Value of dec1 is " + dec1);
Console.WriteLine("Rounded value of " + dec1 +
" is " + Math.Round(dec1));
// Case-2
// A double value whose fractional part is
// greater than the halfway between two
// consecutive integers
Decimal dec2 = 12.785m;
Console.WriteLine("Value of dec2 is " + dec2);
Console.WriteLine("Rounded value of " + dec2 +
" is " + Math.Round(dec2));
}
}
Value of dec1 is 12.345
Rounded value of 12.345 is 12
Value of dec2 is 12.785
Rounded value of 12.785 is 13
Math.Round(Decimal，Int32)
此方法将十进制值舍入为指定数量的小数位数。
句法：
public static decimal Round(decimal x, Int32 y)
范围：
x: A decimal number which is to be rounded. Type of this parameter is System.Decimal.
y: It is the number of fractional digits in the returned value. Type of this parameter is System.Int32.
返回类型：返回最接近x的整数，该整数包含与y相等的小数位数，返回类型为System.Decimal 。
异常：如果y的值小于0或大于15，则此方法将提供ArgumentOutOfRangeException；如果结果超出Decimal的范围，则此方法将提供OverflowException。
例子：
// C# program to demonstrate the
// Math.Round(Decimal, Int32) method
using System;
class Geeks {
// Main Method
static void Main(string[] args)
{
// Case - 1
// The value of digit after specified
// number is less than 5 & Here y = 3
Decimal dx1 = 12.2234565m;
// Output value will be 12.223
Console.WriteLine("Rounded value of " + dx1 +
" is " + Math.Round(dx1, 3));
// Case - 2
// The value of digit after specified
// number is greater than 5 & Here y = 4
Decimal dx2 = 12.8734765m;
// Output value will be 12.8735
Console.WriteLine("Rounded value of " + dx2 +
" is " + Math.Round(dx2, 4));
}
}
Rounded value of 12.2234565 is 12.223
Rounded value of 12.8734765 is 12.8735
注意：上面的十进制值代码以类似于Double值的方式工作。十进制类型和Double类型之间的唯一区别在于精度的概念，即在Double的情况下，精度为64位，在Decimal精度的情况下为128位。
参考： https://docs.microsoft.com/zh-cn/dotnet/api/system.math.round?view=netframework-4.7.2