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C#数学的意外行为。圆形的

.net-core .net c#

0

Sergey · 技术社区 · 2 年前

我有代码:

Math.Round(45.4545m, 2, MidpointRounding.AwayFromZero)

结果是 45.45 。看起来应该是 45.46 具有 MidpointRounding.AwayFromZero 。我做错了什么?

45.46 而不是 45.45 具有 中点舍入。Away FromZero

1 回复 | 直到 2 年前

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StuperUser 2 年前

从…起 MidpointRounding documentation :

四舍五入到最接近的数字的策略,当一个数字在另外两个数字之间时,它会向离零最近的数字四舍五舍五入。

将45.4545四舍五入到2位小数意味着你要取45.45,并决定如何四舍四入.004。正如格里弗斯将军在评论中所说,这还不到另外两个的一半,它更接近于.00,而不是0.01,所以它将四舍五入到45.45,而不是45.46。

以下代码:

Console.WriteLine($"{Math.Round(45.451m, 2, MidpointRounding.AwayFromZero)} = Math.Round({45.451m}, 2, MidpointRounding.AwayFromZero)");
Console.WriteLine($"{Math.Round(45.452m, 2, MidpointRounding.AwayFromZero)} = Math.Round({45.452m}, 2, MidpointRounding.AwayFromZero)");
Console.WriteLine($"{Math.Round(45.453m, 2, MidpointRounding.AwayFromZero)} = Math.Round({45.453m}, 2, MidpointRounding.AwayFromZero)");
Console.WriteLine($"{Math.Round(45.454m, 2, MidpointRounding.AwayFromZero)} = Math.Round({45.454m}, 2, MidpointRounding.AwayFromZero)");
Console.WriteLine($"{Math.Round(45.455m, 2, MidpointRounding.AwayFromZero)} = Math.Round({45.455m}, 2, MidpointRounding.AwayFromZero)");
Console.WriteLine($"{Math.Round(45.456m, 2, MidpointRounding.AwayFromZero)} = Math.Round({45.456m}, 2, MidpointRounding.AwayFromZero)");

给出输出:

45.45 = Math.Round(45.451, 2, MidpointRounding.AwayFromZero)
45.45 = Math.Round(45.452, 2, MidpointRounding.AwayFromZero)
45.45 = Math.Round(45.453, 2, MidpointRounding.AwayFromZero)
45.45 = Math.Round(45.454, 2, MidpointRounding.AwayFromZero)
45.46 = Math.Round(45.455, 2, MidpointRounding.AwayFromZero)
45.46 = Math.Round(45.456, 2, MidpointRounding.AwayFromZero)

你可能在想 Math.Floor method ,请参阅及其在问题中的使用示例 Rounding down to 2 decimal places in c#

对于您问题中给出的示例:

Console.WriteLine($"{Math.Floor((45.4545) * 100) / 100} = Math.Floor((45.4545) * 100) / 100");
Console.WriteLine($"{Math.Floor((45.4541) * 100) / 100} = Math.Floor((45.4541) * 100) / 100");
Console.WriteLine($"{Math.Floor((45.4542) * 100) / 100} = Math.Floor((45.4542) * 100) / 100");
Console.WriteLine($"{Math.Floor((45.4543) * 100) / 100} = Math.Floor((45.4543) * 100) / 100");
Console.WriteLine($"{Math.Floor((45.4544) * 100) / 100} = Math.Floor((45.4544) * 100) / 100");
Console.WriteLine($"{Math.Floor((45.4545) * 100) / 100} = Math.Floor((45.4545) * 100) / 100");
Console.WriteLine($"{Math.Floor((45.4546) * 100) / 100} = Math.Floor((45.4546) * 100) / 100");

给出输出:

45.45 = Math.Floor((45.4545) * 100) / 100
45.45 = Math.Floor((45.4541) * 100) / 100
45.45 = Math.Floor((45.4542) * 100) / 100
45.45 = Math.Floor((45.4543) * 100) / 100
45.45 = Math.Floor((45.4544) * 100) / 100
45.45 = Math.Floor((45.4545) * 100) / 100
45.45 = Math.Floor((45.4546) * 100) / 100