Path: utzoo!attcan!uunet!husc6!bbn!uwmcsd1!csd4.milw.wisc.edu!markh
From: markh@csd4.milw.wisc.edu (Mark William Hopkins)
Newsgroups: comp.lang.pascal
Subject: Number-string conversions
Message-ID: <5817@uwmcsd1.UUCP>
Date: 17 May 88 00:43:33 GMT
Sender: daemon@uwmcsd1.UUCP
Reply-To: markh@csd4.milw.wisc.edu (Mark William Hopkins)
Organization: University of Wisconsin-Milwaukee
Lines: 135


     While the issue is "on the table", I feel it appropriate to give a few 
procedures to show how the conversions take place when Pascal reads & writes
in a text file.

READING INTEGERS FROM TEXT:
     procedure ReadInt(var T : text; var I : integer);
     var
	Sign : char;
     begin
	(*** SKIP SPACES ***)
	while T^ = ' ' do get(T);

        (*** GET THE SIGN ***)
	if T^ in ['+','-'] then begin
	   read(T, Sign)
        end
	else Sign := '+';

	(*** CONVERT THE STRING TO AN INTEGER ***)
	I := 0;
	while T^ in ['0'..'9'] do begin
	   I := 10*I + ord(T^) - ord('0');
	   get(T)
        end;

	(*** ADJUST FOR THE SIGN ***)
	if Sign = '-' then I := -I
     end;

READING REAL NUMBERS FROM TEXT:
(The syntax allowed by this procedure is slightly more liberal 
 than that which standard Pascal allows for.)

     procedure ReadReal(var T : text; var R : real);
     var 
	Exponent : integer;
	Power    : real;
     begin
	(*** CONVERT THE INTEGER PART ***)
	ReadInt(T, R);

	(*** CONVERT THE DECIMAL PART ***)
	if T^ = '.' then begin
	   get(T);
	   Power := 1; 
	   while T^ in ['0'..'9'] do begin
	      Power := Power / 10;
	      R := R + ( ord(T^) - ord('0') ) * Power;
	      get(T)
           end
        end;

	(*** CONVERT THE EXPONENT PART ***)
	if T^ in ['e','E'] then begin
	   get(T);
	   ReadInt(T, Exponent);
	   while Exponent > 0 do begin
	      Exponent := Exponent - 1; R := R * 10
           end;
	   while Exponent < 0 do begin
	      Exponent := Exponent + 1; R := R / 10
           end
        end
     end;	

FORMATTING INTEGERS INTO TEXT:
     procedure WriteInt(T : text; I : integer; FieldWidth : integer);
     var
	Sign : char;
	Size, Exponent : integer;
     begin
	(*** DETERMINE THE SIGN ***)
	if I < 0 then begin
	   Sign := '-'; I := -I
        end
	else if I > 0 then Sign := '+'
	else Sign := '0';
        
	(*** DETERMINE THE SIZE OF THE INTEGER STRING ***)
	Exponent := 1; Size := 0;
	while (Exponent < I) do begin
	   Exponent := 10 * Exponent; Size := Size + 1
        end;

        (*** PAD THE INTEGER TO THE LEFT, IF NECESSARY ***)
	if FieldWidth > Size then begin
	   while FieldWidth > Size + 1 do begin
	      FieldWidth := FieldWidth - 1; write(T, ' ')
           end;
	   if Sign = '+' then write(T, ' ')
        end;

	(*** CONVERT THE NUMBER TO A STRING ***)
	if Sign = '+' then write(T, ' ')
	else if Sign = '-' then write(T, '-')
	else if Sign = '0' then write(T, '0'); 
	else while Size > 0 do begin
	   Size := Size - 1;
	   Exponent := Exponent / 10;
	   write(T, chr(I mod Exponent + ord('0')) );
	   I := I div Exponent
        end
     end;

FORMATTING REALS TO TEXT:
(F1, F2 are the two field widths used for formatting real numbers and
 rounding them to the desired number of decimal places.)

     procedure WriteReal(var T : text; R : real; FW1, FW2 : integer);
     var
	Mantissa : integer;
        Decimal : real;
     begin
	Mantissa := trunc(R); Decimal := R - Mantissa;

	(*** The field width FW1 includes the decimal part and decimal ***)
	(*** point in it.  Therefore the integer part is written out   ***)
	(*** with a field width of FW1 - FW2 - 1.                      ***)

	WriteInt(T, Mantissa, FW1 - FW2 - 1);
	if FW2 > 0 then begin
	   write(T, '.');
	   while FW2 > 1 do begin
	      FW2 := FW2 - 1;
	      Decimal := Decimal * 10;
	      write(T, chr( trunc(Decimal) + ord('0') ) );
	      Decimal := Decimal - trunc(Decimal)
           end;

	   (*** ROUND THE LAST DECIMAL DIGIT ***)
           Decimal := Decimal * 10;
	   write(T, chr( round(Decimal) + ord('0') ) )
        end
     end