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C# double decimal 四舍五入

发布时间 2023-11-27 21:36:34作者: Coder-9527

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using System;
using System.Collections.Generic;
using System.Linq;

public class Program
{
  public static void Main()
  {
    // 先看看double类型 通过Math.Round取两位小数得到什么
    Console.WriteLine( Math.Round(2.345d, 2));    //2.35
    // 再看看decimal类型通过Math.Round取两位小数得到什么
    Console.WriteLine( Math.Round(2.345m, 2));    //2.34
	
    // 对decimal类型，采用了银行家舍入算法：四舍六入五考虑，五后非空就进一，五后为空看奇偶，五前为偶应舍去，五前为奇要进一
    Console.WriteLine( Math.Round(2.3451m, 2));    //2.35 五后非空就进一
    Console.WriteLine( Math.Round(2.345m, 2));     //2.34 五后为空看奇偶，五前为偶应舍去
    Console.WriteLine( Math.Round(2.335m, 2));     //2.34 五前为奇要进一
	
    // 而对于double类型，没那么多讲究，直接满五进一
    Console.WriteLine( Math.Round(2.3451d, 2));    //2.35
    Console.WriteLine( Math.Round(2.345d, 2));     //2.35
    Console.WriteLine( Math.Round(2.335d, 2));     //2.34
    Console.WriteLine( Math.Round(2.334d, 2));     //2.33
	
    // 再来看一个容易疏忽的格式化问题，不管是double还是decimal类型，ToString("0.00")都会做四舍五入
    Console.WriteLine( 2.345d.ToString("0.00"));    //2.35
    Console.WriteLine( 2.345m.ToString("0.00"));    //2.35

    // 对于decimal类型
    Console.WriteLine( Math.Round(2.345m, 2, MidpointRounding.AwayFromZero));    //2.35
    Console.WriteLine( Math.Round(2.345m, 2, MidpointRounding.ToEven));          //2.34
    Console.WriteLine( Math.Round(2.375m, 2, MidpointRounding.AwayFromZero));    //2.38
    Console.WriteLine( Math.Round(2.375m, 2, MidpointRounding.ToEven));          //2.38
	
    // 不让四舍五入，而切掉后面的小数位，
    var pre = 1.4665m;
    var cut = pre - (pre % 0.01M);
    Console.WriteLine(cut.ToString("0.00"));          //1.46
    cut = pre - (pre % 0.001M);
    Console.WriteLine(cut.ToString("0.000"));         //1.466
  }
}