您有一个声明(例如，if 或 while)，就在您发布的代码之前, 没有花括号.

You have a statement (if or while, for example), right before the code you posted, without curly braces.

例如:

if (somethingIsTrue) 
{    
   var user= new ApplicationUser { 
       UserName = model.myUser.Email,
       Email = model.myUser.Email ,
   };
}

是正确的，但是下面的代码:

is correct, but the code below:

if (somethingIsTrue) 
   var user = new ApplicationUser { 
      UserName = model.myUser.Email,
      Email = model.myUser.Email ,
   };

将导致 CS1023:嵌入的语句不能是声明或标记的语句.

will result in CS1023: Embedded statement cannot be a declaration or labeled statement.

根据@codefrenzy，原因是新声明的变量将立即超出范围，除非它包含在块语句中，可以从中访问它.

The reason, according to @codefrenzy, is that the newly declared variable will immediately go out of scope, unless it is enclosed in a block statement, where it can be accessed from.

不过在以下情况下编译会通过.

The compilation will pass in the following cases though.

如果你只初始化一个类型的新实例，而不声明一个新变量:

If you only initialize a new instance of a type, without declaring a new variable:

if (somethingIsTrue) 
   new ApplicationUser { 
       UserName = model.myUser.Email,
       Email = model.myUser.Email ,
   };

或者如果您为现有变量赋值:

or if you assign a value to an existing variable:

ApplicationUser user;

if (somethingIsTrue) 
   user = new ApplicationUser { 
       UserName = model.myUser.Email,
       Email = model.myUser.Email ,
   };