如何正确评估此if语句 [英] How do I get this if statement to properly evaluate

问题描述

我正在做一个涉及生日计划中的try-catch块的家庭作业。虽然我的大部分内容已经停止，但我仍然需要使用if语句，因此程序会在少于31天的时间内正确评估。



< pre lang =c ++> if （（month = 4 ， 6 ， 9 ， 11 ）&&（date> 30 ））
throw invalidDay（）;

每当我尝试运行它时，它会向我抛出invalidDay（）。如果我从程序中删除它，该程序可以找到。我环顾四周但却找不到任何东西，所以我想知道是否有人可以帮助我？



我尝试了什么：



我试过删除程序中的代码，我尝试过使用||运算符，我试过限制if语句的大小（即：month = 4&& date> 30）

解决方案

你没有，因为有几个原因：

1）Equals是一个赋值运算符：你根本不应该在if语句中使用它，并且你不能为一个变量分配四个值。

2）即使您使用了比较运算符==，也可以根据四个值进行检查，它不是在此列表中运算符，而C ++没有运算符。

尝试：

  if （（month ==  4  || month ==  6  || month ==  9  ||月==  11 ）&& date>  30 ）
 {
 ... 

I'm working on a homework assignment involving try-catch blocks in a birthday program. While I have most of it down I'm stuck at an if statement I need to use so the program evaluates properly for months that have less than 31 days.

if ((month = 4, 6, 9, 11) && (date > 30))
			throw invalidDay();

Whenever I try to run it, it throw's the invalidDay() at me. If I remove it from the program, the program works find. I looked around but couldn't really find anything so I was wondering if someone might be able to help me?

What I have tried:

I have tried deleting the code from the program, I have tried using the || operator, I have tried limiting the size of the if statement(ie: month = 4 && date > 30)

解决方案

You don't, for several reasons:
1) Equals is an assignment operator: you shouldn't use it in an if statement at all, and you can't assign four values to a single variable.
2) Even if you used the comparison operator "==", you can;t check it against four values, it isn't an "in this list" operator, and C++ doesn't have one.
Try:

if ((month == 4 || month == 6 || month == 9 || month == 11) && date > 30)
   {
   ...

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