Ulam spiral (for primes): Difference between revisions

=== using FreePascal ===

{{works with|FreePascal|version 3.2.0 }}

<lang Pascal>

PROGRAM Ulam.pas;

{$IFDEF FPC}

{$mode objfpc}{$H+}{$J-}{R+}

{$ELSE}

{$APPTYPE CONSOLE}

{$ENDIF}

USES

Crt,

SysUtils ;

CONST

SIZE = 9 ;

TYPE

D2Arr = array of array of string ;

FUNCTION IsPrime ( n: integer ): boolean ;

VAR

i: integer;

BEGIN

IF ( n < 2 ) THEN Exit ( False ) ;

IF ( n = 2 ) THEN Exit ( True ) ;

IF ( n mod 2 = 0 ) THEN Exit ( False ) ;

FOR i := 3 TO Trunc ( Sqrt ( n ) ) DO

IF ( n mod i = 0 ) THEN Exit( False ) ;

IsPrime := True ;

END;

PROCEDURE Init2DArr ( Arr: D2Arr ) ;

VAR

j: integer;

mid: integer = SIZE div 2 ;

BEGIN

FOR j:= 1 to SIZE - mid - 1 DO

BEGIN

Arr [ mid - j ] [ mid - j ] := '.' ;

Arr [ mid - j ] [ mid + j ] := '.' ;

Arr [ mid + j ] [ mid - j ] := '.' ;

Arr [ mid + j ] [ mid + j - 1 ] := '.' ;

END;

END;

PROCEDURE Advance ( var Turn_cnt, x, y: integer ) ;

VAR

dir: array [ 0..3, 0..1 ] of shortint =

( ( 1, 0 ), ( 0, -1 ), ( -1, 0 ), ( 0, 1 ) ) ;

BEGIN

x := Abs ( x + dir [ Turn_cnt mod 4 ][ 0 ] ) ;

y := Abs ( y + dir [ Turn_cnt mod 4 ][ 1 ] ) ;

END;

PROCEDURE Add2DArr ( Arr: D2Arr ) ;

VAR

cnt: integer = 1 ;

Turn_cnt: integer = 0 ;

x: integer = SIZE div 2 ;

y: integer = SIZE div 2 ;

BEGIN

WHILE ( cnt < SIZE * SIZE ) DO

BEGIN

Advance ( Turn_cnt , x , y ) ;

Inc ( cnt ) ;

IF ( Arr [ x ] [ y ] = '.' ) THEN

BEGIN

Arr [ x ] [ y ] := '' ;

inc ( Turn_cnt ) ;

END;

IF ( IsPrime ( cnt ) ) THEN

Arr [ x ] [ y ] := IntToStr ( cnt ) ;

END;

END;

PROCEDURE Show2DArr ( Arr: D2Arr ; glyph : Boolean ) ;

VAR

x, y: integer ;

BEGIN

WriteLn ;

FOR y := Low ( Arr ) TO High ( Arr ) DO

BEGIN

FOR x := Low ( Arr [ y ] ) to High ( Arr [ y ] ) DO

IF length ( Arr [ x ] [ y ] ) > 0 THEN

IF glyph THEN Write ( '′' : 3 )

ELSE Write ( Arr [ x ] [ y ] : 3 )

ELSE Write ( ' ' : 3) ;

WriteLn;

END;

WriteLn;

END;

VAR

Arr: D2Arr;

BEGIN

SetLength ( Arr, SIZE, SIZE ) ;

Init2DArr ( Arr ) ;

Add2DArr ( Arr ) ;

Show2DArr ( Arr , False ) ;

Show2DArr ( Arr , True ) ;

END.

</lang>JPD 2021/06/14