C++ opencv Moment

#include "opencv2/highgui/highgui.hpp"
#include "opencv2/imgproc/imgproc.hpp"
#include <iostream>
#include <stdio.h>
#include <stdlib.h>

using namespace cv;
using namespace std;

Mat src; Mat src_gray;
int thresh = 100;
int max_thresh = 255;
RNG rng(12345);

/// Function header
void thresh_callback(int, void*);

/** @function main */
int main(int argc, char** argv)
{
VideoCapture cap(0);

while (1)
{
cap >> src;
/// Convert image to gray and blur it
cvtColor(src, src_gray, CV_BGR2GRAY);
blur(src_gray, src_gray, Size(3, 3));

/// Create Window
char* source_window = "Source";
namedWindow(source_window, CV_WINDOW_AUTOSIZE);
imshow(source_window, src);

createTrackbar(" Canny thresh:", "Source", &thresh, max_thresh, thresh_callback);
thresh_callback(0, 0);
if (waitKey(30) == 27)
break;
}
return(0);
}

/** @function thresh_callback */
void thresh_callback(int, void*)
{
Mat canny_output;
vector<vector<Point> > contours;
vector<Vec4i> hierarchy;

/// Detect edges using canny
Canny(src_gray, canny_output, thresh, thresh * 2, 3);
/// Find contours
findContours(canny_output, contours, hierarchy, CV_RETR_TREE, CV_CHAIN_APPROX_SIMPLE, Point(0, 0));

/// Get the moments
vector<Moments> mu(contours.size());
for (int i = 0; i < contours.size(); i++)
{
mu[i] = moments(contours[i], false);
}

///  Get the mass centers:
vector<Point2f> mc(contours.size());
for (int i = 0; i < contours.size(); i++)
{
mc[i] = Point2f(mu[i].m10 / mu[i].m00, mu[i].m01 / mu[i].m00);
}
/// Draw contours
Mat drawing = Mat::zeros(canny_output.size(), CV_8UC3);
for (int i = 0; i< contours.size(); i++)
{
drawContours(drawing, contours, i, Scalar(0,0,255), 1, 8, hierarchy, 0, Point());
circle(drawing, mc[i], 4, Scalar(0,255,125), -1, 8, 0);
}

/// Show in a window
namedWindow("Contours", CV_WINDOW_AUTOSIZE);
imshow("Contours", drawing);

/// Calculate the area with the moments 00 and compare with the result of the OpenCV function
printf("\t Info: Area and Contour Length \n");
for (int i = 0; i< contours.size(); i++)
{
printf(" * Contour[%d] - Area (M_00) = %.2f - Area OpenCV: %.2f - Length: %.2f \n", i, mu[i].m00, contourArea(contours[i]), arcLength(contours[i], true));
drawContours(drawing, contours, i, Scalar(0,255,0), 1, 8, hierarchy, 0, Point());
circle(drawing, mc[i], 4, Scalar(255,0,0), -1, 8, 0);
}
}