注意项

避免滥用：Fortran 90引入了结构化编程的概念，切记不要滥用goto语句
明确标签：在使用goto语句时，标签要明确
避免跳转过多：过多的跳转会增加代码的复杂性和可读性
避免跳转到循环内部：在循环内部使用goto语句可能会导致程序陷入无限循环或者跳出循环
谨慎使用跳转到其他子程序：在跳转到其他子程序时，需要确保目标子程序的执行顺序和状态是正确的

goto is considered bad practice

Code Readability

The use of goto makes the code less readable because it introduces jumping points or labels that disrupt the linear flow of code

Debugging Difficulties

Tracing and debugging errors become more challenging since the execution flow can jump around unpredictably. This makes it harder to identify the source of bugs, leading to longer debugging sessions.

Program Structure and Maintainability

The use of goto ends to encourage spaghetti-like code(结构上完全不可理解的系统) with tangled control flow. This lack of structure makes the program difficult to maintain and modify over time. A well-organized codebase with clearly defined functions and control flow enhances readability and understandability.

goto使用实例

goto代替loop

program goto_loop
    implicit none
    integer :: i

    i = 1
10  if (i <= 10) then
        print *, i
        i = i + 1
        goto 10
        write(*,*) "this sentence just under goto"
    end if
    write(*,*) "this sentence just under end if"
    read(*,*)
end program goto_loop

Fortran 中的 goto 语句-LMLPHP

goto进入loop内部

program goto_example
    implicit none
  
    integer :: i

    i = 1

10  continue

    print *, "i =", i

    i = i + 1

    if (i <= 5) then
        goto 10
    end if

    print *, "Loop finished"
    read(*,*)
end program goto_example

goto在子程序

注意：
- fortran 90 不支持从子程序 goto 到主程序中去

program goto_example
    implicit none

    print *, "Starting program"

    call subprogram

    print *, "Exiting program"
    read(*,*)

end program goto_example
    
subroutine subprogram
        implicit none
        integer :: i

        print *, "Entering subprogram"

    10  do i = 1, 5
            print *, "Loop iteration:", i

            goto 20
        end do

    20  print *, "Reached label 20"

        print *, "Exiting subprogram"
end subroutine subprogram

goto优势

goto语句在下列情况中有显著的优势
- 跳出多层循环：使用goto语句可以直接跳转到指定的标签处，从而避免了使用复杂的逻辑结构或者引入额外的变量来控制循环的退出。
- 错误处理：使用goto语句可以直接跳转到错误处理的标签处，从而简化了错误处理的逻辑。

跳出多重循环

program example
    implicit none
    integer :: i, j, k

    do i = 1, 10
      do j = 1, 10
         do k = 1, 10
            if (k == 5) then
                goto 10
            endif
            print *, i, j, k
         enddo
       enddo
     enddo


10  print *, "Exited loop at k = 5"
    read(*,*)
end program example

错误处理

program error_handling
    implicit none
    
    integer :: num, result
    
    write(*, *) "input an integer here:"
    read(*, *) num
    
    if (num < 0) then
        goto 10
    end if
    
    result = num * num
    
    write(*, *) "the square of your input number:", result
    
    goto 20
    
10  write(*, *) "Negative number is not allowed!"
    
20  write(*,*)"program is over.press any key to exit!"
    read(*,*)
end program error_handling