您需要将字符串（arg）转换为整数。

You'll need to convert the string (arg) into an integer.

program print_
   integer :: i, iarg
   character(len = 32) :: arg
   i = 1   
   Do 
      call get_command_argument(i, arg)
      if ( len_trim(arg) == 0) exit
          write(*,*) trim(arg)
          read(arg,"(I)") iarg
          write(*,*) iarg**2
          i = i + 1
   end do
end program print_