{+++++++++++++++++++++++++++++++++++++}
       {+	 STRING TO INTEGER	    +}
       {+++++++++++++++++++++++++++++++++++++}

Function IVAL( var st: dstring; { alphanumeric string to be converted }
	       var int: integer { returned integer }
	      ): integer;
{
   error_status := IVAL( alphanumeric, returned_integer );

RETURNS:
   error_status
    > 0    NUMERIC STRING  and int = integer number
    = 0    NON-NUMERIC STRING
    = -1   OVERFLOW

EXAMPLE:
    write( 'Chose one answer only: ' );
    readln( answer );
    err := IVAL( answer, n );
    if err>0 then <statement1>
    else begin
      if err=0 then <non-numeric string>
      if err<0 then <overflow>
    end;
}
label 1,2;
const	zero = 48; { ORD('0'); }
var	inx, len: integer;
	signed, negating: boolean;
	ch: char;
	special,
	numeric: set of char;
begin
  numeric := ['0'..'9'];
  special := numeric + ['+','-'];
  signed := false;
  negating := false;
  int := 0;
{+++ SCAN STRING FOR NON-NUMERIC CHARS +++}
  len := length(st);
  for inx:=1 to len do begin
    ch := st[inx];
    if ( ch IN numeric ) then {EXIT} goto 2
    else if ( ch IN ['+','-'] ) and ( inx<len ) then
      if ( st[inx+1] IN numeric ) then {EXIT} goto 2;
  end{for};
  inx := 0; { NON-NUMERIC STRING }
2: if ( inx=0 ) then {terminate} goto 1;

  for inx:=inx to len do begin
	ch := st[inx];
	if ( ch IN special ) then
	   begin
	     if ( ch IN numeric ) then begin
	       if ( int<3276 ) or ((int=3276) and (ch<'8')) then
		   int := int * 10 + ord(ch) - zero
	       else begin
		   int := maxint;
		   inx := -1;
		   {EXIT} goto 1;
	       end;
	       signed := true
	     end
	     else
		   case ch of
		   '+': if ( signed ) then {terminate} goto 1
			else signed := true;
		   '-': if ( signed ) then {terminate} goto 1
			else begin
			   negating := true;
			   signed := true
			end
		   end{case}
	   end
	else
	  {terminate} goto 1
  end{for};
1: {terminate}
  IVAL := inx; { RETURN CODE }
  if negating then int := -int
end{ of IVAL };
rminate} goto 1
  end{for};
1: {terminate}
  IVAL := inx; { RETURN CODE }
  if negatin