在Fortran 90中，是否不可能在新变量的声明语句中引用先前声明的变量？(In Fortran 90, is it impossible to refer to previously-declared variables in the declaration statement of a new variable?)

 在Fortran中，变量的声明语句是否可以引用先前声明的变量？ 例如，当我尝试以下操作时： 
 
PROGRAM test3
  IMPLICIT NONE

  INTEGER :: a=2286
  INTEGER :: b=a/3

  WRITE(*,*) a, b
END PROGRAM test3
 
 我收到编译时错误消息： 
 
test3.f90:5.16:

  INTEGER :: b=a/3
                1
Error: Parameter 'a' at (1) has not been declared or is a variable, which
does not reduce to a constant expression
 
 另一方面，如果我在与声明b不同的语句中将b赋值给a / 2 ，它将编译并运行良好： 
 
PROGRAM test3
  IMPLICIT NONE

  INTEGER :: a=2286
  INTEGER :: b
  b=a/3

  WRITE(*,*) a, b
END PROGRAM test3
 
 这给了我正确的输出： 
 
2286         762
 
 为什么会出现这种情况 - 先前声明的变量不能包含在新变量的声明语句中？ 难道我做错了什么？ 或者这只是一个“Fortran生活事实”？ 
 
 非常感谢您的宝贵时间！ 

In Fortran, is it possible for declaration statements for variables to refer to previously-declared variables? For example, when I try the following:
 
PROGRAM test3
  IMPLICIT NONE

  INTEGER :: a=2286
  INTEGER :: b=a/3

  WRITE(*,*) a, b
END PROGRAM test3
 
I get a compile-time error message:
 
test3.f90:5.16:

  INTEGER :: b=a/3
                1
Error: Parameter 'a' at (1) has not been declared or is a variable, which
does not reduce to a constant expression
 
On the other hand, if I assign b to a/2 in a statement separate from the declaration of b, it compiles and runs fine:
 
PROGRAM test3
  IMPLICIT NONE

  INTEGER :: a=2286
  INTEGER :: b
  b=a/3

  WRITE(*,*) a, b
END PROGRAM test3
 
which gives me the correct output:
 
2286         762
 
Why is this the case--that previously-declared variables cannot be included in declaration statements of new variables? Am I doing something wrong? Or is this just a "Fortran fact of life"?
 
Thank you very much for your time!

原文：https://stackoverflow.com/questions/6510161