update samples: waitKey() usage

Original commit is a5f19f7dd6ae5bc93f73e0417a9e0bfd34c01672

samples/cpp/tutorial_code/ImgTrans/HoughCircle_Demo.cpp

@@ -90,7 +90,7 @@ int main(int argc, char** argv)
     // infinite loop to display
     // and refresh the content of the output image
     // until the user presses q or Q
-    int key = 0;
+    char key = 0;
     while(key != 'q' && key != 'Q')
     {
         // those paramaters cannot be =0
@@ -102,7 +102,7 @@ int main(int argc, char** argv)
         HoughDetection(src_gray, src, cannyThreshold, accumulatorThreshold);
 
         // get user key
-        key = waitKey(10);
+        key = (char)waitKey(10);
     }
 
     return 0;

samples/cpp/tutorial_code/ImgTrans/Remap_Demo.cpp

@@ -40,9 +40,9 @@ int main( int, char** argv )
   for(;;)
   {
     /// Each 1 sec. Press ESC to exit the program
-    int c = waitKey( 1000 );
+    char c = (char)waitKey( 1000 );
 
-    if( (char)c == 27 )
+    if( c == 27 )
       { break; }
 
     /// Update map_x & map_y. Then apply remap

samples/cpp/tutorial_code/ImgTrans/copyMakeBorder_demo.cpp

@@ -23,9 +23,6 @@ RNG rng(12345);
  */
 int main( int, char** argv )
 {
-
-  int c;
-
   //![load]
   src = imread( argv[1], IMREAD_COLOR ); // Load an image
 
@@ -59,13 +56,12 @@ int main( int, char** argv )
   for(;;)
        {
          //![check_keypress]
-         c = waitKey(500);
-
-         if( (char)c == 27 )
+         char c = (char)waitKey(500);
+         if( c == 27 )
            { break; }
-         else if( (char)c == 'c' )
+         else if( c == 'c' )
            { borderType = BORDER_CONSTANT; }
-         else if( (char)c == 'r' )
+         else if( c == 'r' )
            { borderType = BORDER_REPLICATE; }
          //![check_keypress]
 

samples/cpp/tutorial_code/ImgTrans/filter2D_demo.cpp

@@ -25,8 +25,6 @@ int main ( int, char** argv )
   int kernel_size;
   const char* window_name = "filter2D Demo";
 
-  int c;
-
   //![load]
   src = imread( argv[1], IMREAD_COLOR ); // Load an image
 
@@ -45,9 +43,9 @@ int main ( int, char** argv )
   int ind = 0;
   for(;;)
        {
-         c = waitKey(500);
+         char c = (char)waitKey(500);
          /// Press 'ESC' to exit the program
-         if( (char)c == 27 )
+         if( c == 27 )
            { break; }
 
          //![update_kernel]