OpenCV Trackbar example code in webcam video

OpneCVTrackBarInWebcam.cpp

http://study.marearts.com/2016/07/opencv-30-trackbar-simple-example-in.html
#include "opencv2/opencv.hpp"
#include < iostream>
using namespace cv;
using namespace std;

int g_slider; //slider pos value
int g_slider_max; //slider max value

void on_trackbar(int, void*)
{
 printf("%d\n", g_slider);
}


int main()
{
 Mat edges;
 VideoCapture cap = VideoCapture(0);

 if (!cap.isOpened()) return -1; 
 //set
 g_slider = 0;
 g_slider_max = 255;
 namedWindow("edges", 1);

 //make trackbar call back
 createTrackbar("TrackbarName", "edges", &g_slider, g_slider_max, on_trackbar);

 for (;;)
 {
  Mat frame;
  cap >> frame; // get a new frame from camera
  cvtColor(frame, edges, CV_BGR2GRAY);
  GaussianBlur(edges, edges, Size(7, 7), 1.5, 1.5);
  Canny(edges, edges, g_slider, 30, 3);
  imshow("edges", edges);
  if (waitKey(30) >= 0)
 break;
 }

 return 0;
}
 

http://study.marearts.com/2016/07/opencv-30-trackbar-simple-example-in.html