module mianji
   implicit none
contains
   function fun(filename) result(total)
   implicit none
   character(len=79)::filename
   integer,parameter::fileid=10
   real,dimension(1:23)::a,b
   real::s
   integer::i
   real::area=0
   real::total
   logical::alive
   inquire(file=filename,exist=alive)
   if(alive)then
   open(fileid,file=filename,status='old')
   do i=1,23
     read(fileid,*)a(i),b(i)
   end do
   write(*,'(23f6.3)')(a(i),i=1,23)
   write(*,'(23f8.4)')(b(i),i=1,23)
   else
   write(*,*)'文件不存在'
   end if
   do i=1,22
     s=((b(i+1)+b(i))/2)*(a(i+1)-a(i))
     area=area+s
   end do
   total=area
   write(*,*)'area=',total
   end function fun
end module
program jian
   use mianji
   implicit none
   character(len=79)::filename1,filename2
   real::afilename1,afilename2,atotal
   write(*,*)'filename1'
   read(*,'(A79)')filename1
   write(*,*)'filename2'
   read(*,'(A79)')filename2
   afilename1=fun(filename1)
   afilename2=fun(filename2)
   atotal=afilename2-afilename1
   print*,afilename1
   print*,afilename2
   write(*,*)'cl=',atotal
end program jian
分开计算时afilename1=-0.7092733，afilename2=-2.587754E-02。用上面程序计算得到的afilename1=-0.7092733，afilename2=-0.7351311，afilename2是错的。为什么afilename2差这么多，是不是格式设置的问题？
望您指教！