为什么我需要在任何地方声明函数的类型？ [英] Why do I need to declare the type of a function everywhere I use it?

问题描述

 程序功能测试
隐式无
真正:: x， 
 print *，输入数字到方块
读取（*，*）x 
 print *，square（x）
结束程序功能测试
 
 
实函数square（x）
 real :: x 
 square = x * x 
结束函数平方
  

为什么我需要声明 square 为 real 内部程序functiontest ？我还没有在其定义中声明它是一个真实函数？

为什么FORTRAN的作者会这样做设计决定？

解决方案

不，实际上在你的例子中你没有声明它是一个 / code>，但它是该程序的外部函数。如果你在程序中定义了你的函数，如下所示，或者把它放在模块和中使用 d it，你并不需要指定它是一个真实函数两次。



 程序functiontest 
 implicit none 
 real :: x 
 print *，输入一个数字到方块
 read（*，*）x 
 print *，square（x ）
 
包含
实函数square（x）
 real :: x 
 square = x * x 
结束函数square 
结束程序函数测试
  

至于为什么它也按照您编写它的方式工作，它是为了向后兼容Fortran 77 。

Consider the following FORTRAN program:

program functiontest
    implicit none
    real :: x, square
    print *, "Enter a number to square"
    read (*,*) x
    print *, square(x)
end program functiontest


real function square(x)
    real :: x
    square = x * x
end function square

Why do I need to declare square to be real inside program functiontest? Haven't I already declared it a real function in its definition?

Why did the authors of FORTRAN make this design decision?

解决方案

No, actually in your example you haven't declared it a real function inside the program, but it's an external function to the program. If you defined your function inside the program, as follows, or put it in a module and used it, you wouldn't have to specify it's a real function twice.

program functiontest
    implicit none
    real :: x
    print *, "Enter a number to square"
    read (*,*) x
    print *, square(x)

contains
    real function square(x)
        real :: x
        square = x * x
    end function square
end program functiontest

As for why it also works the way you wrote it, it is for backwards compatibility with Fortran 77.

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