How to start camera in OpenCV and draw a rectangle on a detection? Nullpointer exception.

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I want to start my Webcam and draw a Rectangle based on the regions returned by face detection. The compiler of Code::Blocks says no error while compiling. If i want to "Run" the Code the webcam started and in a few second after stoped it and i get this Error in Terminal:

http://imageshack.us/photo/my-images/835/20130423173054486x346sc.png/

So i have the following code:

#include "/usr/local/include/opencv/cv.h"
#include "/usr/local/include/opencv/highgui.h"

#include <iostream>
#include <cstdio>

using namespace std;
using namespace cv;

CvRect *r;

const string haarcascade_face = "/usr/local/share/OpenCV/haarcascades/haarcascade_frontalface_alt.xml";
const string haarcascade_eye = "/usr/local/share/OpenCV/haarcascades/haarcascade_eye_tree_eyeglasses.xml";

////String window_name = "Capture - Face detection";

CvHaarClassifierCascade* cascade;
CvMemStorage* storage;

void detectAndDisplay( IplImage* img);


int main()
{
    CascadeClassifier cascade_face, cascade_eye;
    char c;

    cascade = (CvHaarClassifierCascade*)cvLoad("/usr/local/share/OpenCV/haarcascades/haarcascade_frontalface_alt.xml");
    CvCapture *capture = 0;



    IplImage *frame;


    if(!cascade_face.load(haarcascade_face))
    {
        cout << "[ERROR]: Could not load classifier cascade Face" <<endl;
        return -1;
    }

    if(!cascade_eye.load(haarcascade_eye))
    {
        cout << "[ERROR]: Could not load classifier cascade Eye" <<endl;
        return -1;
    }

    capture = cvCaptureFromCAM(0); // select camera
    if(capture == NULL)
    {
        cout << "[ERROR] No camera found!" << endl;
        return -1;
    }


    // loop forever till ESC
    for(;;)
    {
        // capture a frame from the camera
        frame = cvQueryFrame(capture);

        // display it
        if(!frame) break;


            detectAndDisplay(frame);


        // test for ESC
        c = cvWaitKey(33);
        if(c == 27 /* ESC */)
           break;
    }

    return 0;
}


void detectAndDisplay(IplImage* img)
{

    int i;

    CvSeq* faces = cvHaarDetectObjects(img, cascade, storage, 1.1, 3, CV_HAAR_DO_CANNY_PRUNING, cvSize (100, 100));


    for(i = 0; i<(faces ? faces->total:0); i++)
    {

         r=(CvRect*)cvGetSeqElem(faces,i);
         cvRectangle(img,
                     cvPoint(r->x, r->y),
                     cvPoint(r->x + r->width, r->y + r->height),
                     CV_RGB(255,0,0), 1, 8, 0);
                     }


   cvShowImage("Capture - Face Detection", img);
}

I dont know what the problem is, can someone help me solve this problem?

Thank you for helping me!!!