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 int x,y;
  dbRandomize(dbTimer());
   x=dbRND(639);
   y=dbRND(479);
  
  int ULX;
  int ULY;
  int LRX;
  int LRY;
  DWORD blue = dbRGB(0,0,255);
  DWORD green = dbRGB(0,255,0);
  DWORD yellow = dbRGB(255,255,0);

  ULX=x-50;
  ULY=y-50;
  
  LRX=x+50;
  LRY=y+50;
  dbInk(yellow,yellow);
  dbBox(ULX,ULY,LRX,LRY); 

   const int srad =50;
   int radius;
   for(int count=50;count>0 ;count--){
	radius=srad -count;  
      if (count>=30)
	  {dbInk(green,green);}
	  else {
		  dbInk(blue,blue);}
	dbCircle(x,y,radius);
      } 

#include <DarkGDK.h>

#pragma warning(disable: 4244) // conversion from '<x>' to '<y>', possible loss of data

void FilledCircle( int cx, int cy, int r )
{
    // precalculate the square of the radius - this is the hypotenuse
    int i = r * r;

    // calculate the size of the central square
    int s = r * 0.70710678;      // this magic number is sin(45)

    // draw it
    dbBox( cx-s, cy-s, cx+s+1, cy+s+1 );
    ++s;

    // loop through the bit we have not yet drawn
    for ( int y = s; y <= r; ++y )
    {
        int x = sqrt( (float)(i - ( y * y )) );

        // draw top and bottom
        dbBox( cx-x, cy-y, cx+x+1, cy-y+1 );
        dbBox( cx-x, cy+y, cx+x+1, cy+y+1 );

        // draw left and right
        dbBox( cx-y, cy-x, cx-y+1, cy+x+1 );
        dbBox( cx+y, cy-x, cx+y+1, cy+x+1 );
    }
}

void DarkGDK()
{
    dbSyncOn();
    dbSyncRate(60);

    int Radius = 20;

    while (LoopGDK())
    {
        dbCLS();
        FilledCircle( dbMouseX(), dbMouseY(), Radius );
        if (dbUpKey() && Radius < 100) ++Radius;
        if (dbDownKey() && Radius > 1) --Radius;

        dbSetCursor(0, 0);
        dbPrint( (LONGLONG) Radius );

        dbSync();
    }
}