Problem 2

#if defined(UNICODE) && !defined(_UNICODE)
    #define _UNICODE
#elif defined(_UNICODE) && !defined(UNICODE)
    #define UNICODE
#endif

#include <tchar.h>
#include <windows.h>
#include <cmath>

int Round ( double x )
{
    return (int) ( x + 0.5 );
}


void swappoints ( int &x1 , int &y1 , int &x2 , int &y2)
{
    int temp = x1 ;
    x1 = x2 ;
    x2 = temp ;
    temp = y1 ;
    y1 = y2 ;
    y2 = temp;
}

void DrawLine ( HDC hdc , int xs , int ys , int xe , int ye , COLORREF c )
{
    int dx = xe - xs , dy = ye - ys ;
    if ( abs(dx) > abs(dy) )
    {
        double m = (double) dy / dx ;
        if ( xs > xe)
            swappoints ( xs , ys , xe , ye);
        int x = xs ;
        double y = ys;
        SetPixel(hdc , xs , ys , c);
        while ( x < xe )
        {
            x++;
            y+=m;
            SetPixel(hdc , x , Round(y),c);
        }
    }
        else
        {
            double m = (double) dx / dy ;
        if ( ys > ye)
            swappoints ( xs , ys , xe , ye);
        int x = xs ;
        double y = ys;
        SetPixel(hdc , xs , ys , c);
        while ( y < ye )
        {
            y++;
            x+=m;
            SetPixel(hdc , Round(x) , y ,c);
        }
    }

}

void Draw8points ( HDC hdc , int x , int y , int xc , int yc , COLORREF c)
{
    SetPixel(hdc , xc + x , yc + y , c);
    DrawLine(hdc , xc , yc , xc + x , yc + y , RGB(255,0,0));
    SetPixel(hdc , xc - x , yc + y , c);
    DrawLine(hdc , xc , yc , xc - x , yc + y , RGB(0,255,0));
    SetPixel(hdc , xc - x , yc - y , c);
    DrawLine(hdc , xc , yc , xc - x , yc - y , RGB(255,250,0));
    SetPixel(hdc , xc + x , yc - y , c );
    DrawLine(hdc , xc , yc , xc + x , yc - y , RGB(255,0,255));
    SetPixel(hdc , xc + y , yc + x , c);
    DrawLine(hdc , xc , yc , xc + y , yc + x , RGB(0,255,255));
    SetPixel(hdc , xc - y , yc + x , c);
    DrawLine(hdc , xc , yc , xc - y , yc + x , RGB(255,255,255));
    SetPixel(hdc , xc - y , yc - x , c);
    DrawLine(hdc , xc , yc , xc - y , yc - x , RGB(255,169,175));
    SetPixel(hdc , xc + y , yc - x , c);
    DrawLine(hdc , xc , yc , xc + y , yc - x , RGB(123,123,123));

}

void DrawCircle ( HDC hdc , int xc , int yc , int R , COLORREF c )
{

    double x = 0 , y = R ;
    Draw8points( hdc , x , y , xc , yc , c );
    double d = 1 - R ;
    while ( x < y )
    {
        if ( d < 0 )
        {
            d += 2 * x + 3 ;
            x++ ;
        }
        else
        {
            d += 2 * ( x - y ) + 5 ;
            x++ ;
            y-- ;
        }
        Draw8points(hdc , Round (x) , Round (y) , xc , yc , c);
    }

}






/*  Declare Windows procedure  */
LRESULT CALLBACK WindowProcedure (HWND, UINT, WPARAM, LPARAM);

/*  Make the class name into a global variable  */
TCHAR szClassName[ ] = _T("CodeBlocksWindowsApp");

int WINAPI WinMain (HINSTANCE hThisInstance,
                     HINSTANCE hPrevInstance,
                     LPSTR lpszArgument,
                     int nCmdShow)
{
    HWND hwnd;               /* This is the handle for our window */
    MSG messages;            /* Here messages to the application are saved */
    WNDCLASSEX wincl;        /* Data structure for the windowclass */

    /* The Window structure */
    wincl.hInstance = hThisInstance;
    wincl.lpszClassName = szClassName;
    wincl.lpfnWndProc = WindowProcedure;      /* This function is called by windows */
    wincl.style = CS_DBLCLKS;                 /* Catch double-clicks */
    wincl.cbSize = sizeof (WNDCLASSEX);

    /* Use default icon and mouse-pointer */
    wincl.hIcon = LoadIcon (NULL, IDI_APPLICATION);
    wincl.hIconSm = LoadIcon (NULL, IDI_APPLICATION);
    wincl.hCursor = LoadCursor (NULL, IDC_ARROW);
    wincl.lpszMenuName = NULL;                 /* No menu */
    wincl.cbClsExtra = 0;                      /* No extra bytes after the window class */
    wincl.cbWndExtra = 0;                      /* structure or the window instance */
    /* Use Windows's default colour as the background of the window */
    wincl.hbrBackground = (HBRUSH) COLOR_BACKGROUND;

    /* Register the window class, and if it fails quit the program */
    if (!RegisterClassEx (&wincl))
        return 0;

    /* The class is registered, let's create the program*/
    hwnd = CreateWindowEx (
           0,                   /* Extended possibilites for variation */
           szClassName,         /* Classname */
           _T("Code::Blocks Template Windows App"),       /* Title Text */
           WS_OVERLAPPEDWINDOW, /* default window */
           CW_USEDEFAULT,       /* Windows decides the position */
           CW_USEDEFAULT,       /* where the window ends up on the screen */
           544,                 /* The programs width */
           375,                 /* and height in pixels */
           HWND_DESKTOP,        /* The window is a child-window to desktop */
           NULL,                /* No menu */
           hThisInstance,       /* Program Instance handler */
           NULL                 /* No Window Creation data */
           );

    /* Make the window visible on the screen */
    ShowWindow (hwnd, nCmdShow);

    /* Run the message loop. It will run until GetMessage() returns 0 */
    while (GetMessage (&messages, NULL, 0, 0))
    {
        /* Translate virtual-key messages into character messages */
        TranslateMessage(&messages);
        /* Send message to WindowProcedure */
        DispatchMessage(&messages);
    }

    /* The program return-value is 0 - The value that PostQuitMessage() gave */
    return messages.wParam;
}


/*  This function is called by the Windows function DispatchMessage()  */
int xc , yc , x , y  ;
int counter = 0 ;
bool startpaint = false ;


PAINTSTRUCT ps ;
LRESULT CALLBACK WindowProcedure (HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    switch (message)                  /* handle the messages */
    {
        case WM_DESTROY:
            PostQuitMessage (0);       /* send a WM_QUIT to the message queue */
            break;

        case WM_LBUTTONDOWN:
            if ( counter == 0)
            {
            xc = LOWORD(lParam);
            yc = HIWORD(lParam);
            counter++ ;
            }
            else
            {
            x = LOWORD(lParam);
            y = HIWORD(lParam);
            counter-- ;
            startpaint = true ;
            }
            break;

        case WM_PAINT:
            if ( startpaint == true )
            {
                BeginPaint( hwnd , &ps );
                double R =  sqrt( pow( x - xc , 2.0 ) + pow( y - yc , 2.0) ) ;
                DrawCircle ( ps.hdc , xc , yc , R , RGB(0,0,255));
                EndPaint( hwnd , &ps );
            }
                break;




        default:                      /* for messages that we don't deal with */
            return DefWindowProc (hwnd, message, wParam, lParam);
    }

    return 0;
}