errors in samples/cpp removed

samples/cpp/create_mask.cpp

@@ -36,6 +36,8 @@ int minx,miny,maxx,maxy,lenx,leny;
 
 int channel;
 
+void mouseHandler(int, int, int, int, void*);
+
 void mouseHandler(int event, int x, int y, int, void*)
 {
 
@@ -123,6 +125,13 @@ void mouseHandler(int event, int x, int y, int, void*)
 
 int main(int argc, char **argv)
 {
+
+    if(argc != 2)
+    {
+        cout << "usage: " << argv[0] << " <input_image>" << endl;
+        exit(1);
+    }
+
     Mat src = imread(argv[1]);
 
 	minx = INT_MAX; miny = INT_MAX; maxx = INT_MIN; maxy = INT_MIN;