Free Pascal

Implementation of programming language Pascal

Free Pascal (aka FPC Pascal or FPK Pascal) is a 32 and 64 bit Pascal compiler, written itself in Pascal.

Free Pascal is compatible with Borland Pascal 7 and most versions of Borland Delphi, but has number of additional features (operator overloading, function overloading, global properties, etc…).

The packages and runtime library come under a modified Library GNU Public License to allow the use of static libraries when creating applications. The compiler source itself comes under the GNU General Public License.

Lazarus - standard IDE for Free Pascal
Lazarus - standard IDE for Free Pascal

Links:

Examples:

Factorial:

Example for versions Free Pascal 2.0.4, Free Pascal 2.2.0, Turbo Pascal 4.0, Turbo Pascal 5.0, Turbo Pascal 5.5, Turbo Pascal 6.0, Turbo Pascal 7.0, gpc 20070904

This example uses recursive factorial definition.

Note that this example works in all given implementations of Pascal, but it produces slightly different results. In gpc everything works perfectly. Turbo Pascal and Free Pascal have arithmetic overflow for factorial of numbers greater than 12, but Free Pascal reports an error:

13! = Runtime error 215 at $004013C7
$004013C7
$00401449
$004063E0

while Turbo Pascal doesn’t detect the error and simply prints wrong values:

13! = 1932053504
14! = 1278945280
15! = 2004310016
16! = 2004189184

This example doesn’t work in Turbo Pascal 3.0 and earlier due to absence of longint data type in these versions.

In GNU Pascal this program works without any problems. 

program factorial;

function fact(n: integer): longint;
begin
    if (n = 0) then
        fact := 1
    else
        fact := n * fact(n - 1);
end;

var
    n: integer;

begin
    for n := 0 to 16 do
        writeln(n, '! = ', fact(n));
end.

Hello, World!:

Example for versions Free Pascal 2.0.4, Free Pascal 2.2.0, Turbo Pascal 1.0, Turbo Pascal 2.0, Turbo Pascal 3.0, Turbo Pascal 4.0, Turbo Pascal 5.0, Turbo Pascal 5.5, Turbo Pascal 6.0, Turbo Pascal 7.0, gpc 20070904 
program helloworld;

begin
    writeln('Hello, World!');
end.

Fibonacci numbers:

Example for versions Free Pascal 2.0.4, Free Pascal 2.2.0, Turbo Pascal 1.0, Turbo Pascal 2.0, Turbo Pascal 3.0, Turbo Pascal 4.0, Turbo Pascal 5.0, Turbo Pascal 5.5, Turbo Pascal 6.0, Turbo Pascal 7.0, gpc 20070904

This example uses recursive definition of Fibonacci numbers. 

program fibonacci;

function fib(n:integer): integer;
begin
    if (n <= 2) then
        fib := 1
    else
        fib := fib(n-1) + fib(n-2);
end;

var
    i:integer;

begin
    for i := 1 to 16 do
        write(fib(i), ', ');
    writeln('...');
end.

Factorial:

Example for versions Free Pascal 2.0.4, Free Pascal 2.2.0, Turbo Pascal 1.0, Turbo Pascal 2.0, Turbo Pascal 3.0, Turbo Pascal 4.0, Turbo Pascal 5.0, Turbo Pascal 5.5, Turbo Pascal 6.0, Turbo Pascal 7.0, gpc 20070904

This example is exactly the same as main recursive example for Pascal implementations, except for that it uses real data type to store factorial values. Command writeln(f:-1:0) outputs the floating point number f with 0 digits after decimal point and left-justifies it. 

program factorial;

function fact(n: integer): real;
begin
    if (n = 0) then
        fact := 1
    else
        fact := n * fact(n - 1);
end;

var
    n: integer;

begin
    for n := 0 to 16 do
        writeln(n, '! = ', fact(n):-1:0);
end.

Quadratic equation:

Example for versions Free Pascal 2.0.4, Free Pascal 2.2.0, Turbo Pascal 1.0, Turbo Pascal 2.0, Turbo Pascal 3.0, Turbo Pascal 4.0, Turbo Pascal 5.0, Turbo Pascal 6.0, gpc 20070904

Pascal has built-in complex data type complex, but using it is inconvenient in this case, because writeln can’t output complex numbers directly, and functions Re and Im would have to be used. In this example calculations are done in real numbers. Library function halt (added in Extended Pascal) exits current block (in later versions it is replaced with exit). 

program Quadratic;

var
   A,B,C,D: integer;

begin
   write('A = ');
   readln(A);
   if (A=0) then
   begin
      writeln('Not a quadratic equation.');
      halt;
   end;
   write('B = ');
   readln(B);
   write('C = ');
   readln(C);
   D := B*B-4*A*C;
   if (D=0) then
   begin
      writeln('x = ',-B/2.0/A);
      halt;
   end;
   if (D>0) then
   begin
      writeln('x1 = ',(-B+Sqrt(D))/2.0/A);
      writeln('x2 = ',(-B-Sqrt(D))/2.0/A);
   end
   else
   begin
      writeln('x1 = (',-B/2.0/A,',',Sqrt(-D)/2.0/A,')');
      writeln('x2 = (',-B/2.0/A,',',-Sqrt(-D)/2.0/A,')');
   end;
end.

CamelCase:

Example for versions Free Pascal 2.2.0, Turbo Pascal 4.0, Turbo Pascal 5.0, Turbo Pascal 5.5, Turbo Pascal 6.0, gpc 20070904

This example is similar to previous one, but uses sets of characters for letter check. This makes the code more readable.

Note that in Turbo Pascal series this program works only with Turbo Pascal 4.0 and higher due to the fact that earlier versions didn’t have char datatype. 

program Camelcase;

var
    text, cc: string[100];
    c: char;
    i: integer;
    lastSpace: boolean;
    upper, lower: set of char;

begin
    upper := ['A'..'Z'];
    lower := ['a'..'z'];
    readln(text);
    lastSpace := true;
    cc := '';
    for i := 1 to Length(text) do
    begin
        c := text[i];
        if (c in lower) or (c in upper) then
        begin
            if (lastSpace) then { convert to uppercase }
            begin
                if (c in lower) then
                    c := chr(ord(c) - 32);
            end
            else { convert to lowercase }
                if (c in upper) then
                    c := chr(ord(c) + 32);
            cc := cc + c;
            lastSpace := false;
        end
        else
            lastSpace := true;
    end;
    writeln(cc);
end.

CamelCase:

Example for versions Free Pascal 2.2.0, Turbo Pascal 4.0, Turbo Pascal 5.0, Turbo Pascal 5.5, Turbo Pascal 6.0, gpc 20070904

This example processes the string char by char, and works with ASCII-codes to figure out whether they are lower- or uppercase letters. ord returns ASCII-code of a character, while chr converts given ASCII-code into a character. String capacity is omitted and thus set to 255 by default.

Note that in Turbo Pascal series this program works only with Turbo Pascal 4.0 and higher due to the fact that earlier versions didn’t have char datatype. 

program Camelcase;

var
    text, cc: string;
    c: char;
    i: integer;
    lastSpace: boolean;

begin
    readln(text);
    lastSpace := true;
    cc := '';
    for i := 1 to Length(text) do
    begin
        c := text[i];
        if ((c >= #65) and (c <= #90)) or ((c >= #97) and (c <= #122)) then
        begin
            if (lastSpace) then
            begin
                if ((c >= #97) and (c <= #122)) then
                    c := chr(ord(c) - 32);
            end
            else
                if ((c >= #65) and (c <= #90)) then
                    c := chr(ord(c) + 32);
            cc := cc + c;
            lastSpace := false;
        end
        else
            lastSpace := true;
    end;
    writeln(cc);
end.