[文件读写] 新人求助，想去除一个文件中负数

Program main
  Use DFile_Mod
  Implicit None
  Real , allocatable :: a(:,:)
  Character(len=512) :: cStr
  Real    :: r  
  integer :: FILE_IN , i , nRow , nCol
  Open( NewUnit = FILE_IN , File = "text.asc" )
  nRow = GetFileN( FILE_IN ) - 2 !//获得文件行数 
  Read( FILE_IN , * ) !//跳过第一行
  Read( FILE_IN , '(a512)' ) cStr!//读取第三行
  nCol = GetDataN( cStr ) - 8 !//获得第三行有多少列
  write( *, '("Row:",g0," Col: ",g0)' ) nRow , nCol
  Allocate( a( nCol , nRow ) )
  Backspace( FILE_IN ) !//退回到第三行
   open( 11 , file ="tx1.txt")
    write( 11 , * )"  depth          temp          sal           turb  "
  Do i = 1 , nRow
    Read( FILE_IN , * ) r ,r, r, r, a( : , i )
    write( 11 , * ) a(:,i)
  End Do
  Deallocate( a )
  Close( FILE_IN )
End Program main

Program www_fcode_cn
  implicit none
  character(len=512) :: c
  character(len=1)   :: s
  integer :: FILE_IN , FILE_OUT , k , i
  real    :: DepSM
  Open( NewUnit = FILE_IN , File = "text.asc" )
  Open( NewUnit = FILE_OUT, File = "text.txt" )
  Read( FILE_IN , 100 ) c
  Write( FILE_OUT , 99 ) trim(c)
  Do
    Read( FILE_IN , 100 , ioStat = k ) c
    if ( k /= 0 ) exit
    Read( c , * ) i , i , i , s , DepSM
    If ( DepSM > 0.0 ) then
      Write( FILE_OUT , 99 ) trim(c)
    End If
  End Do
  Close( FILE_IN )
  Close( FILE_OUT )
100 format(a512)
99  format(a)
End Program www_fcode_cn