C＃布尔方法帮助！ [英] C# boolean method help!

问题描述

我一直在编写一个项目的代码，我想知道如何创建一个方法（IsEnrolled）来返回一个布尔值（需要使用if语句。）这个方法必须返回一个真实的语句，学生是注册的，如果学生没有注册，则为假。问题是我的CurrentEnrolledCourse属性是一个字符串，当我创建它时，我不断收到一条错误，上面写着Can not Implicity转换类型'字符串'为'bool'





这是我到目前为止的代码（这只是代码的一部分而不是完整的代码！）

  public   bool  IsEnrolled（）
 {
  if （CurrentEnrolledCourse =  null ）
 {
  return   false ; 
} 
  else  
 {返回  true ; 
} 
} 
 

我尝试了什么：



我试图将字符串转换为bool但是我发现了什么它呢！

解决方案

这是明确的作业，因为需要使用if语句。

显然你需要更熟悉C＃语法; 特别是分配和比​​较运算符。

  public   bool  IsEnrolled（）
 {
  if （CurrentEnrolledCourse ==  null ）
 {
  return   false ; 
} 
 其他 
 {
 返回 真; 
} 
} 

假设学生只有当CurrentEnrolledCourse不为空时才注册。

更好的方法（因为需要使用if语句）：

  public   bool  IsEnrolled（）
 {
  if （CurrentEnrolledCourse ==  null ）
  return   false ; 
  return   true ; 
} 

正确的方式：

  public   bool  IsEnrolled（）
 {
  return ！string。 IsNullOrEmpty（CurrentEnrolledCourse）; 
} 

（它应该是只获取属性。）

< blockquote>将

 CurrentEnrolledCourse 

与null进行比较时输入

 == 

。



试试这个：

  public   bool  IsEnrolled（）
 {
  if （ string  .IsNullOrEmpty（CurrentEnrolledCourse））
 {
  return   false  ; 
} 
 其他 
 {
 返回 真; 
} 
} 

或只需修改你的代码：

  public   bool  IsEnrolled（）
 {
  if （CurrentEnrolledCourse ==  null ）
 {
 < span class =code-keyword> return   false ; 
} 
  else  
 { return  真; 
} 
} 

谢谢，

它应该是

  if （CurrentEnrolledCourse ==  null ） ... 

此外，所有那些if-else都是毫无意义的。你有没有想过这个？您在if下的表达式已经是布尔值，为什么if？这样做：

  public   bool  IsEnrolled（）{ return  CurrentEnrolledCourse！=  null ; } 

不是那么简单吗？ :-)



现在，一点奖金：



让我来告诉你一个老程序员的伎俩：而不是 if（CurrentEnrolledCourse == null）写 if（null == CurrentEnrolledCourse） 。但为什么？两个片段的含义和功能完全相同。所以为什么？考虑一下。让我们说，你再次错误地输入=（赋值）而不是==（相等的比较）。但在第二种形式，编译器会给你一个明确的错误信息，这将帮助你立即发现这个问题;这是因为你真的可以为变量/成员分配null而不能为null赋值，即所谓的立即常量。

-SA

Ive been writing a code for a project and I was wondering how to create a method (IsEnrolled) to return a Boolean value (need to use if statement.) This method will have to return a true statement is student is enrolled and a false if student isn't enrolled. The problem is my CurrentEnrolledCourse property is a string and when I create it I keep getting an error that says "Cannot Implicity convert type 'string' to 'bool'


Here is the code I have so far (This is just part of the code not the complete code!)

public bool IsEnrolled()
{
if (CurrentEnrolledCourse = null)
{
    return false;
}
    else
    { return true;
    }
}

What I have tried:

I have tried to convert string to bool but I havnt found anything on it yet!

解决方案

This is clearly homework since "need to use if statement".
Clearly you need to get more familiar with C# syntax; specifically the assignment and comparison operators.

public bool IsEnrolled()
{
    if (CurrentEnrolledCourse == null)
    {
        return false;
    }
    else
    {
        return true;
    }
}

Assuming the student is enrolled only if the CurrentEnrolledCourse isn't empty.
A better way (since "need to use if statement"):

public bool IsEnrolled()
{
    if (CurrentEnrolledCourse == null)
        return false;
    return true;
}

The right way:

public bool IsEnrolled()
{
    return !string.IsNullOrEmpty(CurrentEnrolledCourse);
}

(And it should be a "get-only" property.)

Put "

==

" while comparing

CurrentEnrolledCourse

with null.

Try this:

public bool IsEnrolled()
        {
            if (string.IsNullOrEmpty(CurrentEnrolledCourse))
            {
                return false;
            }
            else
            {
                return true;
            }
        }

or just modify your code:

public bool IsEnrolled()
{
if (CurrentEnrolledCourse == null)
{
    return false;
}
    else
    { return true;
    }
}

Thanks,

It should be

if (CurrentEnrolledCourse == null) ...

Moreover, all those "if-else" are just pointless. Did you even think of that? Your expression under "if" is already a Boolean, so why "if"? Do just this:

public bool IsEnrolled() { return CurrentEnrolledCourse != null; }

Isn't that simple? :-)

Now, a little bonus:

Let me tell you one old programmer's trick: instead of if (CurrentEnrolledCourse == null) write if (null == CurrentEnrolledCourse). But why? The meaning and functionality of both fragments is exactly the same. So why? Just think about it. Let's say, you again mistakenly typed "=" (assignment) instead of "==" (comparison for equality). But in the second form, the compiler will give you a clear error message which will help you to spot this problem immediately; and this is because you can really assign null to a variable/member and cannot assign anything to the null, which is the so-called immediate constant.

—SA

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