复制构造函数给我加const！

OOP/13Exam/3.4.cpp

@@ -9,7 +9,7 @@ public:
         cout << "Constructor!";
         display();
     }
-    complex(complex &c) : r(c.r), i(c.i) {
+    complex(const complex &c) : r(c.r), i(c.i) {
         cout << "Copy Constructor!";
         display();
     };
@@ -23,14 +23,11 @@ private:
 };
 
 complex complex::operator+(complex c2) {
-    complex result(r + c2.r, i + c2.i);
-    return result;
+    return complex(r + c2.r, i + c2.i);
 }
 
 complex complex::operator-(complex c2) {
-    complex result(r - c2.r, i - c2.i);
-    return result;
-    // return complex(r - c2.r, i - c2.i);
+    return complex(r - c2.r, i - c2.i);
 }
 
 void complex::display() {

OOP/15Exam/3.6.cpp

@@ -12,7 +12,7 @@ public:         // 外部接口
         cout << "Constructor!";
         display();
     }
-    complex(complex &c) : r(c.r), i(c.i) {
+    complex(const complex &c) : r(c.r), i(c.i) {
         // this->num = ++count;
         // cout << "(Num: " << this->num << ")";
 
@@ -37,9 +37,10 @@ private:
 };
 
 complex complex::operator+(complex c2) {
-    complex result(r + c2.r, i + c2.i);
-    return result;
+    // complex result(r + c2.r, i + c2.i);
+    // return result;
 
+    return complex(r + c2.r, i + c2.i);
     // 原文：return complex(r + c2.r, i + c2.i)，不能编译=_=
 }