title: OpenCV C++ error (cvCaptureFromCAM())
body: <p>I was following a tutorial on web for an OpenCV library, and have a problem actually on an early stage. After declaring needed variables to capture a picture from a webcam with the help of "cvCaptureFromCAM(0)" function. 
  After compiling it gives me:
   error: ‘p_capWebcam’ was not declared in this scope</p>
  
  <p>I have seen a plenty of problems with "was not declared in this scope" errors but didn't find a solution.. </p>
  
  <p>Thank you</p>
  
  <pre><code>#include &lt;opencv/highgui.h&gt;
  #include &lt;opencv/cxcore.h&gt;
  #include &lt;opencv/cvaux.h&gt;
  
  #include &lt;stdio.h&gt;
  #include &lt;stdlib.h&gt;
  
  int main(int argc, char* argv[]) {
  
  CvSize size640x480 = cvSize(640, 480); 
  
  CvCapture* p_camWebcam;  
  
  IplImage* p_imgOriginal; 
  IplImage* p_imgProcessed;
  
  CvMemStorage* p_strStorage; 
  
  CvSeq* p_seqCircles;     
  
  float* p_fltXYReadius;    
  
  int i;                    
  char charCheckForEscKey;   
  
  
  
  p_camWebcam = cvCaptureFromCAM(0); 
  
  if(p_capWebcam == NULL) {   
  printf("error: capture is NULL \n");
  getchar();  
  return(-1); 
  }
  }
  </code></pre>