How to draw a circle or rectangle in cpp, example2?

 #include <iostream>
#include <opencv2/opencv.hpp>

using namespace cv;
using namespace std;

// global structure to remember some states changed
// by mouse action and move
struct initRoi
{
    // on off
    int init;

    //initial coordination based on EVENT_LBUTTONDOWN
    int initX;
    int initY;

    // actual coordination
    int actualX;
    int actualY;

    //Selected Rect
    Rect roiRect;

    //Selected Mat roi
    Mat takenRoi;
} SelectedRoi;

//event int is compared to determine action of the mouse EVENT_RBUTTONDOWN
// EVENT_LBUTTONDOWN, EVENT_LBUTTONUP, EVENT_MOUSEMOVE.
// If the event is evauated as happened the global structure SelectedRoi
// is updated.
static void CallBackF(int event, int x, int y, int flags, void* img)
{
//Mouse Right button down
    if (event == EVENT_RBUTTONDOWN)
    {
        cout << "right button " << endl;
        return;
    }
//Mouse Left button down
    if (event == EVENT_LBUTTONDOWN)
    {
        SelectedRoi.initX = x;
        SelectedRoi.initY = y;
        SelectedRoi.init = 1;
        cout << "left button DOWN" << endl;
        return;
    }
//Mouse Left button up
    if (event == EVENT_LBUTTONUP)
    {
        SelectedRoi.actualX = x;
        SelectedRoi.actualX = y;
        cout << "left button UP" << endl;
        return;
    }
//Mouse move coordinates update
    if (event == EVENT_MOUSEMOVE)
    {

        cout << "event mouse move"<< endl;
        SelectedRoi.actualX = x;
        SelectedRoi.actualY = y;
        SelectedRoi.roiRect = Rect(SelectedRoi.initX, SelectedRoi.initY,
                                   SelectedRoi.actualX,  SelectedRoi.actualY);
        return;
    }
}

int main()
{
    // capture
    VideoCapture cap(0);
    // Set initial state for the SelectedRoi structure
//- The init is set = 1 by left button down action
//- This start to display image if (SelectedRoi.init != 0) in main for loop
    SelectedRoi.init = 0;

    for (;;)
    {
        if (!cap.isOpened())
        {
            cout << "Video Capture Fail" << endl;
            break;
        }

        else
        {
            Mat img;
            cap >> img;

            namedWindow("Video", WINDOW_AUTOSIZE);
// mouse call back function, where CallBackF is function
// with parameters event type, x y coorfinates
            setMouseCallback("Video", CallBackF, 0);

            if (SelectedRoi.init != 0)
            {
// draw the rectangle updated by mouse move
                rectangle(img, Rect(SelectedRoi.initX, SelectedRoi.initY,
                                    SelectedRoi.actualX- SelectedRoi.initX, SelectedRoi.actualY- SelectedRoi.initY),
                          Scalar(255, 255, 255), 1, 8, 0);

            }
            imshow("Video", img);
            int key2 = waitKey(20);
        }
    }
}