update samples: waitKey() usage

Original commit is a5f19f7dd6ae5bc93f73e0417a9e0bfd34c01672

samples/cpp/tutorial_code/video/bg_sub.cpp

@@ -23,7 +23,7 @@ using namespace std;
 Mat frame; //current frame
 Mat fgMaskMOG2; //fg mask fg mask generated by MOG2 method
 Ptr<BackgroundSubtractor> pMOG2; //MOG2 Background subtractor
-int keyboard; //input from keyboard
+char keyboard; //input from keyboard
 
 /** Function Headers */
 void help();
@@ -98,7 +98,8 @@ void processVideo(char* videoFilename) {
         exit(EXIT_FAILURE);
     }
     //read input data. ESC or 'q' for quitting
-    while( (char)keyboard != 'q' && (char)keyboard != 27 ){
+    keyboard = 0;
+    while( keyboard != 'q' && keyboard != 27 ){
         //read the current frame
         if(!capture.read(frame)) {
             cerr << "Unable to read next frame." << endl;
@@ -119,7 +120,7 @@ void processVideo(char* videoFilename) {
         imshow("Frame", frame);
         imshow("FG Mask MOG 2", fgMaskMOG2);
         //get the input from the keyboard
-        keyboard = waitKey( 30 );
+        keyboard = (char)waitKey( 30 );
     }
     //delete capture object
     capture.release();
@@ -139,7 +140,8 @@ void processImages(char* fistFrameFilename) {
     //current image filename
     string fn(fistFrameFilename);
     //read input data. ESC or 'q' for quitting
-    while( (char)keyboard != 'q' && (char)keyboard != 27 ){
+    keyboard = 0;
+    while( keyboard != 'q' && keyboard != 27 ){
         //update the background model
         pMOG2->apply(frame, fgMaskMOG2);
         //get the frame number and write it on the current frame
@@ -162,7 +164,7 @@ void processImages(char* fistFrameFilename) {
         imshow("Frame", frame);
         imshow("FG Mask MOG 2", fgMaskMOG2);
         //get the input from the keyboard
-        keyboard = waitKey( 30 );
+        keyboard = (char)waitKey( 30 );
         //search for the next image in the sequence
         ostringstream oss;
         oss << (frameNumber + 1);