Can't draw basic shapes with OpenCV and C++: where is the error?

Question

I'm trying to draw some basic shapes on a blank image using OpenCV and C++. Here's the example code I'm trying to run:

#include <opencv2/core/core.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <opencv2/imgproc.hpp> // drawing shapes
#include <iostream>
#define CV_FILLED   -1

int main( int argc, char** argv )
{
    // First create a black image.
    cv::Mat image(500,500, CV_8UC3, cv::Scalar(0,0,0));
    cv::namedWindow( "Display window", cv::WINDOW_AUTOSIZE );
        cv::imshow( "Display window", image );

        cv::waitKey(0);
    // Check if the image is created successfully.
    if( !image.data ){
        std::cout <<  "Could not open or find the image" << std::endl ;
        exit(EXIT_FAILURE);
    }


    //####################(  Draw Line  )##########################
    cv::Point p1(100,100), p2(200,100);
    cv::Scalar colorLine(0,255,0); // Green
    int thicknessLine = 2;

    cv::line(image, p1, p2, colorLine, thicknessLine);

    //####################(  Draw Circle  )#########################
    // unfilled circle
    cv::Point centerCircle1(250,250);
    int radiusCircle = 30;
    cv::Scalar colorCircle1(0,0,255);
    int thicknessCircle1 = 2;

    cv::circle(image, centerCircle1, radiusCircle, colorCircle1, thicknessCircle1);

    // filled circle
    cv::Point centerCircle2(400,100);
    cv::Scalar colorCircle2(0,100,0);

    cv::circle(image, centerCircle2, radiusCircle, colorCircle2, CV_FILLED);

    //####################(  Draw Rectangle  )#######################
    // unfilled
    cv::Point p3(400,400), p4(450,450);
    cv::Scalar colorRectangle1(0,0,255);
    int thicknessRectangle1 = 3;

    cv::rectangle(image, p3, p4, colorRectangle1,thicknessRectangle1);

    //   filled
    cv::Point p5(100,400), p6(150,450);
    cv::Scalar colorRectangle2(255,0,255);

    cv::rectangle(image, p5, p6, colorRectangle2, CV_FILLED);


    //#################( Draw Shapes on Image )######################
    cv::namedWindow( "Display window", cv::WINDOW_AUTOSIZE );
    cv::imshow( "Display window", image );

    cv::waitKey(0);


    return 0;
}

The output I'm getting looks like this:

While I expect to get this:

It happens whenever I try using cv::circle or cv::rectangle to draw basic shapes. For example, I tried running the following:

// C++ program to demonstrate rectangle
// over a self-formed background image

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

// Drawing shapes
#include <opencv2/imgproc.hpp>

#include <opencv2/highgui/highgui.hpp>
using namespace cv;
using namespace std;

// Driver Code

int main(int argc, char** argv)
{
    // Creating a blank image with
    // white background
    Mat image(500, 500, CV_8UC3,
              Scalar(255, 255, 255));

    // Check if the image is created
    // successfully or not
    if (!image.data) {
        std::cout << "Could not open or "
                  << "find the image\n";

        return 0;
    }

    // Top Left Corner
    Point p1(30, 30);

    // Bottom Right Corner
    Point p2(255, 255);

    int thickness = 2;

    // Drawing the Rectangle
    rectangle(image, p1, p2,
              Scalar(255, 0, 0),
              thickness, LINE_8);

    // Show our image inside a window
    imshow("Output", image);
    waitKey(0);

    return 0;
}

And the result I got was:

Where is the error?