fix bug

ch16/ex16.14.15/Screen.h

@@ -15,7 +15,7 @@ class Screen {
     typedef std::string::size_type pos;
     Screen() = default; // needed because Screen has another constructor
     // cursor initialized to 0 by its in-class initializer
-    Screen(char c):contents(ht * wd, c) { }
+    Screen(char c):contents(H * W, c) { }
     char get() const              // get the character at the cursor
         { return contents[cursor]; }       // implicitly inline
     Screen &move(pos r, pos c);      // can be made inline later
@@ -25,4 +25,12 @@ class Screen {
     std::string contents;
 };
 
+template<unsigned H, unsigned W>
+inline Screen<H, W>& Screen<H, W>::move(pos r, pos c)
+{
+    pos row = r * width;
+    cursor = row + c;
+    return *this;
+}
+
 #endif // SCREEN_H