writeinteger.pl0

{ read and write an integer }

const E_OK = 0, E_INVALID = 1, E_OVERFLOW = 2;

var integer, err, a;

procedure read_integer;
  var c, n, running, sign, i;
begin
  err := E_OK;
  running := 1;
  n := 0;
  sign := 1;
  i := 0;
  while running = 1 do
  begin
    readChar into c;
    { if ( i = 0 and ( c = 43 or c = 45 ) }
    if (i + (c - 43) * (c - 45)) = 0 then
    begin
      if c = 43 then sign := 1
      else if c = 45 then sign := -1;
      readChar into c;
    end;
    { if ( c = -1 or c = 10 ) }
    if ((c + 1) * (c - 10)) = 0 then
    begin
      running := 0;
      integer := n * sign;
      if i = 0 then err := E_INVALID
      else if i > 19 then
        if n < 0 then
          err := E_OVERFLOW;
    end
    { if ( c < 48 or c > 57 ) }
    else if ((c - 48) * (57 - c)) < 0 then
    begin
      err := E_INVALID;
      running := 0;
    end
    else begin
      c := c - 48;
      n := n * 10;
      n := n + c;
      i := i + 1;
    end;
  end;
end;

procedure write_integer;
  var n, m, d, c;
begin
  n := integer;
  d := 1;
  if n < 0 then n := -n;
  while n > 0 do
  begin
    n := n / 10;
    d := d * 10;
  end;
  n := integer;
  if n = 0 then writeChar 48;
  if n < 0 then begin writeChar 45; n := -n end;
  while d >= 10 do
  begin
    d := d / 10;
    m := n / d;
    n := n - m * d;
    c := m + 48;
    writeChar c
  end;
end;

begin
  call read_integer;
  a := 96;
  if err = E_INVALID then
  begin
    writeStr 'invalid\n';
    exit 1;
  end
  else if err = E_OVERFLOW then
  begin
    writeStr 'overflow\n';
    exit 1;
  end
  else
    call write_integer;
  writeChar 10;
end.