一个计算相关的编程思路/方法讨论

楚香饭

看注释
Program main
  Implicit None
  Character(len=8) :: filename  !// 字符串要给长度
  Character(len=8) :: filename1 !// 如果不给长度，默认是1个长度。只能到9，10就不行了
  Integer :: i, j, num
  Real :: a(4), b(4), c(4)
  num=9  ! number of files you want to run
  Open (10, File='IDlist.dat')
  Do j = 1, num
    Read (10, *) filename1
    Open (j, File='c6c8_ID_'//filename1//'.dat', Status='unknown')
    Write (j, '(3f8.3)') 0.0, 0.0, 1.0
  End Do
  Open (20, File='filename.dat')
  Do i = 1, num ! number of files you want to run
    Read (20, *) filename
    Open (30, File='D:\C6\c6_'//trim(adjustl(filename))//'.dat') !// filename 最好 adjustl一下，去除左边的空格
    Open (40, File='D:\C8\c8_'//trim(adjustl(filename))//'.dat') !// trim 只能去除右边的空格
    Do j = 1, num ! number of files you want to run
      Read (30, *) a(:)
      Read (40, *) b(:)
      c(:) = b(:) - a(:)
      Write (a(1), '(3f8.3)') c(2:4)
    End Do
    Close (30)
    Close (40)
  End Do
  Close (20)
  Do j = 1, num
    Close (j)
  End Do
  Close (10)
End Program main

楚香饭

说明你的 c6c8_10.dat 里面没有 10 行呗。
Do J = 1, num  说明至少要读 num 行