Question

double? AssessmentTotal=2.345;
double? AssessmentTotalval = Math.Round((decimal)AssessmentTotal == null ? 0 : AssessmentTotal, 2);

我试图将双倍值整理一下。预期结果为2.35

我收到了构建错误。

错误40最佳重载方法匹配＆＃39; System.Math.Round（double，int）＆＃39;有一些无效的论点

Answer 1

考虑到舍入是一种非廉价的操作，您可以：

double? AssessmentTotalval = AssessmentTotal == null ? 
                    0.0 : 
                    Math.Round(AssessmentTotal.Value, 2, MidpointRounding.AwayFromZero)

如果Math.Round为AssessmentTotal，则完全绕过null。

请注意，此时AssessmentTotalval总是！= null，因此拥有double?

是没用的

请注意，即使使用MidpointRounding.AwayFromZero，否则0.005将成为0而不是0.01。

Answer 2

尝试这样做：

double? AssessmentTotal = 2.345;
double? AssessmentTotalval = Math.Round(AssessmentTotal.GetValueOrDefault(), 2);

您当前的方法存在许多问题。

首先，如果(decimal)AssessmentTotal == null不为null，则条件AssessmentTotal仅计算为true。只要它是null，就会得到一个＆＃34; InvalidOperationException：Nullabl对象必须有一个值。＆＃34;例外。致电AssessmentTotal.GetValueOrDefault()可以避免这个问题。

其次，Math.Round(...)使用double或decimal - 使用0使您的代码可读性降低（并且可能有错误）。您应始终使用0.0 double或0m decimal。在您的情况下，您应该使用0.0，因为您正在处理double。

根据您的评论重新整理49.625，您需要将代码更改为：

double? AssessmentTotal = 49.625;
double? AssessmentTotalval = Math.Round(AssessmentTotal.GetValueOrDefault(), 2, MidpointRounding.AwayFromZero);

MidpointRounding默认值为MidpointRounding.ToEven - 您需要MidpointRounding.AwayFromZero。

Answer 3

你可以像下面这样做。

double? AssessmentTotal=2.345;
double? AssessmentTotalval = AssessmentTotal.HasValue ? Math.Round(AssessmentTotal.Value,2) : (double?)null;

如果您想在AssessmentTotal为null时为0 然后你可以修改上面的代码如下。

double? AssessmentTotal=2.345;
double? AssessmentTotalval = AssessmentTotal.HasValue ? Math.Round(AssessmentTotal.Value,2) : (double?)0;

Answer 4

double? AssessmentTotal=2.345;
double? AssessmentTotalval = Math.Round((decimal)AssessmentTotal == null ? 0 
 : AssessmentTotal.Value, 2);
Console.WriteLine(AssessmentTotalval);

**更正**

如果值为null，则上面的代码抛出错误。以下代码效果更好

double? AssessmentTotalval = AssessmentTotal != null ? Math.Round(AssessmentTotal.Value, 2) : 0;

Answer 5

double? AssessmentTotalval = Convert.ToDouble((AssessmentTotal ?? 0).ToString("N2"));

Math.Round具有双倍值

5 个答案: