Programmi

Conversione di base

Un programma in Fortran 90 che converte un numero da una base ad un'altra

Un programma in Fortran 90 che converte un numero da una base ad un'altra, a cura di Jean Pierre Moreau un Ingegnere Aeronautico con la passione dell'ananalisi numerica.

PROGRAM BASE

integer       ba,bd
character*40  x,y
real*4        r

integer CodeBase, DecodeBase

  print *,''
  print *,' BASE CONVERSION'
  print *,''
  write(*,10,advance='no'); read *, bd
  write(*,20,advance='no'); read *, ba
  x='1'
  do while (x.ne.'0')
    print *,''
    write(*,30,advance='no'); read *, x
    if (x.ne.'0') then
      if (DecodeBase(x,bd,r).ne.0) then
        if (CodeBase(r,ba,y).ne.0) then
          write(*,50)  ba, y
        else
          print *,' Error in coding number.'
        end if
      else
        print *,' Error in decoding number.'
      end if
    end if
  end do

  print *,''
  stop
 
10 format('  Start  Base (2 to 36): ')
20 format('  Arival Base (2 to 36): ')
30 format('  Enter number in start base: ')

50 format('  In base ',I2,': ',A20)

END

!Convert a number from base b to base 10. The function returns
!FALSE if b not in [2..36] or if string x contains invalid
!characters in base b or if result y is too big}
integer Function DecodeBase(x,b,y)
character*(*) x
integer b
real*4  mult
character*1 ch
parameter(XMAXREAL=1.e30)

  DecodeBase=0
  if (b<2.or.b>36) then
    print *,' Base must be between 2 and 36 !'
    return
  end if
  y=0.; mult=1.
  long=LEN_TRIM(x)
  do i=1, long
    k=long+1-i
    ch=x(k:k)
    if (ch<'0'.or.ch>'Z'.or.(ch>'9'.and.ch<'A')) return
    if (ch<='9') then
  j=IACHAR(ch)-IACHAR('0')
    else
  j=IACHAR(ch)-IACHAR('A')+10
    end if
    if (j>=b) return
    y=y+mult*j
    if (mult>XMAXREAL/b) return
    mult=mult*b
  end do
  DecodeBase=1
  return
End

!Convert a number from base 10 to base b. The function returns
!FALSE if b not in [2..36] or if string x contains invalid
!characters in base 10 or if number x is too big
integer Function CodeBase(x,b,y)
integer b
character*(*) y
  CodeBase=0
  if (b<2.or.b>36) then
    print *,' Base must be between 2 and 36 !'
    return
  end if
  y=''
  do while (x>0.)
    n=INT(x-b*INT(x/b))
    if (n<10) then
  y=ACHAR(IACHAR('0')+n)//y
    else
  y=ACHAR(IACHAR('A')+n-10)//y
    end if
    x=INT(x/b)          
  end do
  CodeBase=1
  return
End

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