Fortran 中的函数与子程序-编程知识

Fortran 中的函数与子程序

简介

Fortran 是不区分大小写的
函数（Function）：
- 函数是一段具有输入和输出的代码块，它接受一些输入参数，经过一系列计算后返回一个结果。
  - 在Fortran中，函数的定义以关键字"FUNCTION"开始，以"end function"结束
  - Fortran 90中的函数必须在程序的`contains`块中定义，以便在主程序中调用
子程序（Subroutine）：
- 子程序是一段独立的代码块，它可以被其他代码调用并执行。与函数不同的是，子程序可以不返回任何结果，或者通过参数列表传递结果。在Fortran中，子程序的定义以关键字"SUBROUTINE"开始，后面跟着子程序名和参数列表。子程序体内部可以包含一系列的计算语句，执行完后通过关键字"END SUBROUTINE"结束。

函数实例

exam1：不使用return语句

需要定义返回值

program function_exampleimplicit nonereal :: length, width, areawrite(*,*) "input length:"read(*,*) lengthwrite(*,*) "input width:"read(*,*) widtharea = calculate_area(length, width)write(*,*) "the area of triangle", arearead(*,*)containsfunction calculate_area(length,width) result(area)real, intent(in) :: length, widthreal :: areaarea = length * widthend function calculate_areaend program function_example

exam2：使用return语句

直接定义函数（函数返回值）类型

program return_exampleimplicit nonereal :: num1, num2, averagewrite(*, *) "input two number:"read(*, *) num1, num2average = calculate_average(num1, num2)write(*,*) "the average of the two numbers:", averageread(*,*)containsreal function calculate_average(a, b)real, intent(in) :: a, bcalculate_average = (a + b) / 2.0  return  end function calculate_average
end program return_example

子程序实例

exam1：Simple Subroutine

program mainimplicit nonecall print_message()read(*,*)
end program mainsubroutine print_message()print *, "Hello, World!"
end subroutine print_message

exam2:Subroutine with Arguments

program mainimplicit nonereal :: num1, num2, sumnum1 = 2.5num2 = 3.7call calculate_sum(num1, num2, sum)print *, "The sum is:", sumread(*,*)
end program mainsubroutine calculate_sum(a, b, result)real :: a, b, resultresult = a + b
end subroutine calculate_sum

子程序不是函数，可以理解为按照约定处理一个变量

exam3:Subroutine with Intent

program mainimplicit nonereal :: numbers(5) = [1,2,3,4,5]integer :: icall square_array(numbers,5)do i = 1, 5print *, numbers(i)end doread(*,*)end program mainsubroutine square_array(arr, size)integer, intent(in) :: sizereal, intent(inout) :: arr(size)integer :: ido i = 1, sizearr(i) = arr(i) ** 2end do
end subroutine square_array

或者
- 我们添加了一个size函数

program mainimplicit nonereal :: numbers(5) = [1,2,3,4,5]integer :: iinteger :: jj = size(numbers)call square_array(numbers,j)do i = 1, jprint *, numbers(i)end doread(*,*)end program mainsubroutine square_array(arr, size)integer, intent(in) :: sizereal, intent(inout) :: arr(size)integer :: ido i = 1, sizearr(i) = arr(i) ** 2end do
end subroutine square_array

函数与子程序的发展史

In Fortran, subroutines and functions are used to encapsulate a specific set of instructions that can be called and executed from different parts of a program.
Subroutines are defined using the SUBROUTINE keyword followed by a name, and they do not return any values.
- They are typically used for performing a series of calculations or operations without returning a result. Subroutines can have input parameters, which are variables passed to the subroutine for use within its code.
Functions, on the other hand, are defined using the FUNCTION keyword followed by a name. Functions are used to perform calculations and return a single value as the result.
- They can have input parameters, similar to subroutines, which are used in the calculation.
Both subroutines and functions can be called from other parts of the program using their respective names.
- When calling a subroutine, the program flow jumps to the subroutine code, executes it, and then returns to the calling point.
- When calling a function, the result of the calculation is returned and can be assigned to a variable or used directly in an expression.
在C语言中，存在函数
在Java中，称为方法（method）
在Python中，也有函数（function）
通过区分function和subroutine，Fortran可以更好地满足不同的编程需求。这样的设计可以提高代码的可读性和可维护性，使得程序的逻辑更加清晰明确。
- Function适用于需要返回结果的计算任务
- Subroutine适用于需要执行一系列操作或修改参数值的任务。