Hi i want to use external camera to capture image rather than in build camera [closed]

edit

This is the current part that i'm using. How do i edit it so i can capture video from external camera?? I'm using Asus xtion pro live.

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

using namespace cv;
using namespace std;

 int main( int argc, char** argv )
 {
    VideoCapture cap(0); //capture the video from web cam

     if ( !cap.isOpened() )  // if not success, exit program
 {
     cout << "Cannot open the web cam" << endl;
 return -1;
}
   }