can not draw rectangle simultaneously

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When ı executed code program is not working correctly.I want to start to draw a rectangle when mouse lButton is clicked and finish drawing when lbutton is up. when moving the mouse ,nothing will happen but it have to increase width and height of box.The problem is exactly that: image appearing and first time ( sometimes 2 times ) I am drawing rectangle.but it doesn t seem on screen when I close image window it automatically appears with rectangle. So after restarting image window I can only have one or two rectangles.

Why are there only rectangles?

Why are they occuring when image window restarts?

#include<opencv\cv.h>
#include<opencv\highgui.h>

using namespace cv;
bool drawing=false;
CvRect box;

void drawbox(IplImage * img,CvRect rect )
{
    cvRectangle(img,cvPoint(box.x,box.y),cvPoint(box.x+box.width,box.y+box.height),cvScalar(0,0,200));
}

void mouse( int even,int x,int y,int flag,void * param)
{
    IplImage* out = ( IplImage * ) param;

    switch (even)
    {
    case CV_EVENT_LBUTTONDOWN:
        drawing=true;
        box=cvRect(x,y,0,0);
        break;
    case CV_EVENT_MOUSEMOVE:
        if (drawing)
        {
            if( x>box.x )
                box.width=x-box.x;
            else
                box.width=box.x-x;
            if(y>box.y)
                box.height=y-box.y;
            else
                box.height=box.y-y;
        }
        break;
    case EVENT_LBUTTONUP:
        drawing = false;
        drawbox(out,box);
        break;
    }
}

void main()
{
    IplImage * img= cvLoadImage("c:/lena.jpg");
    box=cvRect(-1,-1,0,0);
    cvNamedWindow("pencere");
    cvSetMouseCallback("pencere",mouse,(void*) img);
    while (true)
    {
        cvShowImage("pencere",img);
        if(drawing) drawbox(img,box); // what changes if I delete this line
        cvWaitKey();
    }
}