update cpp samples and tutorials

samples/cpp/tutorial_code/introduction/display_image/display_image.cpp

@@ -1,7 +1,7 @@
 //! [includes]
-#include <opencv2/core/core.hpp>
+#include <opencv2/core.hpp>
 #include <opencv2/imgcodecs.hpp>
-#include <opencv2/highgui/highgui.hpp>
+#include <opencv2/highgui.hpp>
 
 #include <iostream>
 #include <string>
@@ -16,7 +16,7 @@ using namespace std;
 int main( int argc, char** argv )
 {
     //! [load]
-    string imageName("../data/HappyFish.jpg"); // by default
+    String imageName( "../data/HappyFish.jpg" ); // by default
     if( argc > 1)
     {
         imageName = argv[1];
@@ -28,7 +28,7 @@ int main( int argc, char** argv )
     //! [mat]
 
     //! [imread]
-    image = imread(imageName.c_str(), IMREAD_COLOR); // Read the file
+    image = imread( imageName, IMREAD_COLOR ); // Read the file
     //! [imread]
 
     if( image.empty() )                      // Check for invalid input