修改答案

excersize/ch07.md

@@ -696,8 +696,7 @@ class Screen {
         Screen(pos ht, pos wd):height(ht), width(wd), contents(ht*wd, ' '){ } // 2
         Screen(pos ht, pos wd, char c):height(ht), width(wd), contents(ht*wd, c){ } // 3
 
-        char get
-        () const { return contents[cursor]; }
+        char get() const { return contents[cursor]; }
         char get(pos r, pos c) const { return contents[r*width+c]; }
 
     private:
@@ -954,14 +953,12 @@ pos Screen::size() const
 
 解：
 
-未定义标识符`pos`。应该改为：
-
-```cpp
-Screen::pos Screen::size() const
-{
-    return height * width;
-}
-```
+纠正：错误为 error: extra qualification 'Screen::' on member 'size' [-fpermissive]
+则应该去掉Screen::,改为
+ ```cpp
+ pos size() const{
+            return height * width;
+        }
 
 ## 练习7.34
 如果我们把第256页`Screen`类的`pos`的`typedef`放在类的最后一行会发生什么情况？