diff --git a/README.md b/README.md
index 794b4d3..12b8932 100644
--- a/README.md
+++ b/README.md
@@ -5,3 +5,5 @@
 #### day1: C++简介, ::作用域, namespace 命名空间, using 声明, using 编译指令, 类型转换, struct 类型加强, bool 关键字, 三目运算符增强, const 增强
 
 #### day2: const 和#define 的区别, 引用(reference) 【重要】, 内联函数, 函数的默认值参数, 函数的占位参数, 函数重载和 extern "c", 类与对象的概念, 面向对象程序设计案例
+
+#### day3: 对象的构造与析构, 构造函数的分类与调用, 拷贝构造函数的调用时机, 构造函数的调用规则, 深拷贝和浅拷贝, 多个对象的构造和析构(初始化列表, 类对象作为成员), explicit 关键字(禁止隐式转换), 动态创建对象(malloc/realloc/calloc 在堆中创建空间, new 关键字), 扩展 new 和 delete,
diff --git a/day3/d1.cpp b/day3/d1.cpp
new file mode 100644
index 0000000..f178712
--- /dev/null
+++ b/day3/d1.cpp
@@ -0,0 +1,74 @@
+// 对象的构造与析构
+#include <iostream>
+#include <cstdlib>
+#include <cstring>
+
+using namespace std;
+
+class Animal
+{
+public:
+    Animal();
+    Animal(const char *name, const char *food);
+    ~Animal(); // 析构函数（对象回收时，清理资源）
+
+public:
+    void eat();
+    void say(const char *msg);
+
+private:
+    char *name, *food;
+};
+
+Animal::Animal()
+{
+    name = (char *)malloc(32);
+    food = (char *)malloc(32);
+    strcpy(name, "小动物");
+    strcpy(food, "水");
+}
+
+Animal::Animal(const char *name, const char *food)
+{
+    this->name = (char *)malloc(32);
+    this->food = (char *)malloc(32);
+    strcpy(this->name, name);
+    strcpy(this->food, food);
+}
+
+Animal::~Animal()
+{
+    cout << name << "空间回收" << endl;
+
+    // 回收在构造函数(初始化)中动态分配的空间
+    free(name);
+    free(food);
+}
+
+void Animal::eat()
+{
+    cout << name << "吃: " << food << endl;
+}
+
+void Animal::say(const char *msg)
+{
+    cout << name << "遇到主人: " << msg << endl;
+}
+
+int main()
+{
+    // 尽量使用堆空间创建类的对象： 使用 类指针 和 new 关键字
+    Animal *anm1 = new Animal();
+    anm1->eat();
+
+    // 使用栈空间的情况
+    Animal anm2;
+    anm2.say("小浣熊");
+
+    // 使用括号
+    Animal anm3("小黄", "肉");
+    anm3.eat();
+    anm3.say("旺旺...");
+
+    return 0;
+}
diff --git a/day3/d10.cpp b/day3/d10.cpp
new file mode 100644
index 0000000..cd5ea1e
--- /dev/null
+++ b/day3/d10.cpp
@@ -0,0 +1,60 @@
+// 深拷贝和浅拷贝
+// 深拷贝举例
+#include <iostream>
+#include <cstdlib>
+#include <cstring>
+
+using namespace std;
+
+class Person
+{
+private:
+    char *name;
+    int age;
+
+public:
+    Person(const char *name, int age)
+    {
+        this->name = (char *)malloc(32);
+        strcpy(this->name, name);
+        this->age = age;
+    }
+    Person(const Person &obj) // 深拷贝，重写构造方法
+    {
+        this->name = (char *)malloc(32);
+        strcpy(this->name, obj.name);
+        this->age = obj.age;
+    }
+    ~Person()
+    {
+        if (name != NULL)
+        {
+            free(name);
+        }
+    }
+
+public:
+    void setName(char *name)
+    {
+        strcpy(this->name, name);
+    }
+    void show()
+    {
+        cout << this << "  " << name << ", " << age << endl;
+    }
+};
+
+int main()
+{
+    Person p1("disen", 20);
+    Person p2 = p1;
+    p2.setName("lucy");
+    Person p3 = Person(p2);
+    p3.setName("Jack");
+
+    p1.show();
+    p2.show();
+    p3.show();
+
+    return 0;
+}
diff --git a/day3/d11.cpp b/day3/d11.cpp
new file mode 100644
index 0000000..9422142
--- /dev/null
+++ b/day3/d11.cpp
@@ -0,0 +1,27 @@
+// 多个对象的构造和析构
+// 初始化列表
+#include <iostream>
+
+using namespace std;
+
+class A
+{
+private:
+    int x, y, z;
+    // char *name;
+    string name; // char * 建议替换为 string
+
+public:
+    A(int x, int y, int z, const string &name) : x(x), y(y), z(z), name(name) {}
+    void show()
+    {
+        cout << x << ", " << y << ", " << z << ", " << name << endl;
+    }
+};
+
+int main()
+{
+    A a1(10, 20, 4, "disen");
+    a1.show();
+    return 0;
+}
diff --git a/day3/d12.cpp b/day3/d12.cpp
new file mode 100644
index 0000000..971fcd6
--- /dev/null
+++ b/day3/d12.cpp
@@ -0,0 +1,48 @@
+// 多个对象的构造和析构
+// 类对象作为成员
+#include <iostream>
+
+using namespace std;
+
+class A
+{
+public:
+    A()
+    {
+        cout << "A()" << endl;
+    }
+    A(int x)
+    {
+        cout << "A(int x)" << endl;
+    }
+    ~A()
+    {
+        cout << "~A()" << endl;
+    }
+};
+
+class B
+{
+public:
+    B() // 构造函数用于初始化成员数据，说明成员变量先创建
+    {
+        cout << "B()" << endl;
+    }
+    B(int x)
+    {
+        cout << "B(int x)" << endl;
+    }
+    ~B() // A 的对象在 B 的空间中，A 对象在 B 空间释放之后就失效，失效也会释放空间（调用析构函数）
+    {
+        cout << "~B()" << endl;
+    }
+
+private:
+    A a; // A 类的对象作为 B 类的成员
+};
+
+int main()
+{
+    B b1;
+    return 0;
+}
diff --git a/day3/d13.cpp b/day3/d13.cpp
new file mode 100644
index 0000000..c8479fb
--- /dev/null
+++ b/day3/d13.cpp
@@ -0,0 +1,50 @@
+// 多个对象的构造和析构
+// 类对象作为成员
+// d12 的改造测试
+#include <iostream>
+
+using namespace std;
+
+class A
+{
+public:
+    A()
+    {
+        cout << "A()" << endl;
+    }
+    A(int x)
+    {
+        cout << "A(int x)" << endl;
+    }
+    ~A()
+    {
+        cout << "~A()" << endl;
+    }
+};
+
+class B
+{
+public:
+    B() // 构造函数用于初始化成员数据，说明成员变量先创建
+    {
+        cout << "B()" << endl;
+    }
+    // 成员名:(参数名)
+    B(int x) : a(x) // 指定 a 对象的构造函数进行数据初始化
+    {
+        cout << "B(int x)" << endl;
+    }
+    ~B() // A 的对象在 B 的空间中，A 对象在 B 空间释放之后就失效，失效也会释放空间（调用析构函数）
+    {
+        cout << "~B()" << endl;
+    }
+
+private:
+    A a; // A 类的对象作为 B 类的成员
+};
+
+int main()
+{
+    B b1(1);
+    return 0;
+}
diff --git a/day3/d14.cpp b/day3/d14.cpp
new file mode 100644
index 0000000..246d086
--- /dev/null
+++ b/day3/d14.cpp
@@ -0,0 +1,43 @@
+// explicit 关键字(禁止隐式转换)
+#include <iostream>
+
+using namespace std;
+
+class Person
+{
+private:
+    int age;
+    string name;
+
+public:
+    Person(const char *name, int age = 18)
+    {
+        this->name = name;
+        this->age = age;
+    }
+    // explicit 使得不存在从 "int" 转换到 "Person" 的适当构造函数
+    explicit Person(int age) // 进制 Person p = 值
+    {
+        this->age = age;
+        this->name = "disen";
+    }
+
+public:
+    void show()
+    {
+        cout << name << ", " << age << endl;
+    }
+};
+
+int main()
+{
+    Person p1 = "jack";
+    Person p2 = Person("doken", 9);
+    Person p3 = Person(1);
+    // Person p4 = 2; // 不存在从 "int" 转换到 "Person" 的适当构造函数
+    p1.show();
+    p2.show();
+    p3.show();
+
+    return 0;
+}
diff --git a/day3/d15.cpp b/day3/d15.cpp
new file mode 100644
index 0000000..39c629a
--- /dev/null
+++ b/day3/d15.cpp
@@ -0,0 +1,51 @@
+// 动态创建对象(malloc / realloc / calloc 在堆中创建空间, new 关键字)
+#include <iostream>
+#include <cstdlib>
+
+using namespace std;
+
+class A
+{
+private:
+    int x;
+
+public:
+    A(int x)
+    {
+        this->x = x;
+        cout << "A(int)" << endl;
+    }
+    ~A()
+    {
+        cout << "~A()" << endl;
+    }
+
+public:
+    void init(int x)
+    {
+        this->x = x;
+        cout << "init(int)" << endl;
+    }
+    void clean()
+    {
+        cout << "clean()" << endl;
+    }
+};
+
+int main()
+{
+    // 1) 使用 malloc 方式创建
+    // cout << "A size is " << sizeof(A) << endl;
+    // A *a1 = (A *)malloc(sizeof(A));
+    // // a1->A(20); // 不允许显式调用构造函数
+    // a1->init(20); // 初始化数据
+    // a1->clean();  // 释放数据的空间
+    // a1->~A();     // 析构函数可以显式调用
+    // free(a1);
+
+    // 2) new 方式创建，delete释放
+    A *a1 = new A(1);
+    delete a1; // 用完之后直接 delete 释放空间
+
+    return 0;
+}
diff --git a/day3/d16.cpp b/day3/d16.cpp
new file mode 100644
index 0000000..130d51e
--- /dev/null
+++ b/day3/d16.cpp
@@ -0,0 +1,23 @@
+// 扩展 new 和 delete
+// 数组的 new 和 delete
+#include <iostream>
+
+using namespace std;
+
+int main()
+{
+    // 使用拓展的 new 创建类对象数组
+    int *p = new int[6]{1, 2, 3, 4, 5, 6};
+    for (int i = 0; i < 10; i++)
+    {
+        cout << *(p + i) << endl;
+    }
+    delete[] p; // 释放数组空间
+
+    cout << "--------------------" << endl;
+    for (int i = 0; i < 10; i++)
+    {
+        cout << *(p + i) << endl;
+    }
+    return 0;
+}
diff --git a/day3/d17.cpp b/day3/d17.cpp
new file mode 100644
index 0000000..5431626
--- /dev/null
+++ b/day3/d17.cpp
@@ -0,0 +1,43 @@
+#include <iostream>
+#include <cstdlib>
+
+using namespace std;
+
+class A
+{
+private:
+    string name;
+
+public:
+    A()
+    {
+        cout << "A()" << endl;
+        name = "no name";
+    }
+    A(const string &name)
+    {
+        cout << "A(const string &name)" << endl;
+        this->name = name;
+        cout << "name: " << name << endl;
+    }
+    ~A()
+    {
+        cout << name << "~A()" << endl;
+    }
+};
+
+int main()
+{
+    // A *p = new A[5];
+    // delete[] p;
+    // A *p2 = new A[4]{A("a"), A("b"), A("c"), A("d")};
+    // delete[] p2; // 释放数组中成员对象时，从高(地址)到低(地址)依次释放
+
+    A *a = new A("abc");
+    free(a); // 只是放指针指向的堆空间，不会调用对象的析构函数
+
+    char *a2 = (char *)malloc(sizeof(A));
+    delete a2; // 可以删除简单的 void* 指针
+
+    return 0;
+}
diff --git a/day3/d2.cpp b/day3/d2.cpp
new file mode 100644
index 0000000..98617f0
--- /dev/null
+++ b/day3/d2.cpp
@@ -0,0 +1,35 @@
+// 构造函数的分类与调用
+// 拷贝构造函数
+#include <iostream>
+
+using namespace std;
+
+class A
+{
+
+public:
+    int x;
+
+public:
+    A() {}
+    A(A &other) // 拷贝构造函数
+    {
+        this->x = other.x;
+    }
+};
+
+int main()
+{
+    A a1; // 调用无参的构造函数进行初始化 a1 对象
+    a1.x = 10;
+    cout << "a1 x = " << a1.x << endl;
+
+    A a2(a1); // 使用拷贝构造
+    cout << "a2 x = " << a2.x << endl;
+
+    A *a3 = new A(); // 使用指针和new，在堆空间创建对象
+    // a3->x = 20;
+    cout << "a3 x = " << a3->x << endl;
+
+    return 0;
+}
diff --git a/day3/d3.cpp b/day3/d3.cpp
new file mode 100644
index 0000000..624b54c
--- /dev/null
+++ b/day3/d3.cpp
@@ -0,0 +1,44 @@
+// 构造函数的分类与调用
+#include <iostream>
+
+using namespace std;
+
+class B
+{
+private:
+    int n;
+
+public:
+    // B() { cout << "B()" << endl; }
+    B(int n)
+    {
+        cout << "B(int n)" << endl;
+        this->n = n;
+    }
+    B(const B &other)
+    {
+        cout << "B(B &other)" << endl;
+        this->n = other.n;
+    }
+
+public:
+    void showN()
+    {
+        cout << "n = " << n << endl;
+    }
+};
+
+int main()
+{
+    B b1 = 20; // 隐式调用 B(int n), B(20), 只创建一个对象
+
+    B b2 = B(30); // 显式调用 B(int n)
+
+    B b3 = b2; // 隐式调用 B(B &other)
+
+    B &b4 = b3; // 不会创建空间，只是一个别名
+
+    B b5(b4); // 显式调用 B(B &other)
+
+    return 0;
+}
diff --git a/day3/d4.cpp b/day3/d4.cpp
new file mode 100644
index 0000000..a19e123
--- /dev/null
+++ b/day3/d4.cpp
@@ -0,0 +1,56 @@
+// 构造函数的分类与调用
+#include <iostream>
+#include <bitset>
+
+using namespace std;
+
+class C
+{
+private:
+    int x, y;
+
+public:
+    C(int x)
+    {
+        this->x = x;
+    }
+    C(int x, int y)
+    {
+        this->x = x;
+        this->y = y;
+    }
+    C(const C &other)
+    {
+        this->x = other.x;
+        this->y = other.y;
+    }
+    void show()
+    {
+        cout << "x = " << x << ", y = " << y << endl;
+    }
+    ~C()
+    {
+        cout << this << "释放资源" << endl;
+    }
+};
+
+int main()
+{
+    cout << "C(0,1) 之前" << endl;
+    C(0, 1); // 匿名创建的类对象，创建完后就直接释放了
+    cout << "C(0,1) 之后" << endl;
+
+    C c1(1, 2);
+    c1.show();
+    C c2 = (1, 5); // 使用单参数构造函数 C(int x), 然后将其改为 ", 运算" 后面的值
+    // C c2 = 1;
+    c2.show();
+    C c3 = C(3, 4);
+    c3.show();
+    C c4(c3);
+    c4.show();
+    C &c5 = c4;
+    c5.show();
+
+    return 0;
+}
diff --git a/day3/d5.cpp b/day3/d5.cpp
new file mode 100644
index 0000000..0abd131
--- /dev/null
+++ b/day3/d5.cpp
@@ -0,0 +1,54 @@
+// 创建类对象的指针
+#include <iostream>
+#include <cstdlib>
+#include <cstring>
+
+using namespace std;
+
+class A
+{
+public:
+    char *msg;
+
+public:
+    A()
+    {
+        this->msg = (char *)malloc(30);
+        strcpy(this->msg, "haha");
+    }
+    A(const char *msg)
+    {
+        this->msg = (char *)malloc(30);
+        strcpy(this->msg, msg);
+    }
+    ~A()
+    {
+        cout << this << "release msg : " << this->msg << endl;
+        free(this->msg);
+        // free(this);
+    }
+};
+
+int main()
+{
+    A *a1 = new A;
+    cout << "a1->msg: " << a1->msg << endl;
+
+    A *a2 = new A("disen 666");
+    cout << "a2->msg: " << a2->msg << endl;
+
+    // 【注意】指针释放空间时, 不会自动执行对象的析构函数
+    // 可以通过手动调用 对象的析构方法 或使用 delete
+    a1->~A();
+    free(a1);
+    // a2->~A();
+    // delete a1;
+    delete a2;
+
+    A a3;
+    // 注意: delete 只能删除 new 出来的对象，即对象的指针
+    // A &a4 = a3;
+    // delete &a4;
+
+    return 0;
+}
diff --git a/day3/d6.cpp b/day3/d6.cpp
new file mode 100644
index 0000000..dd1bf34
--- /dev/null
+++ b/day3/d6.cpp
@@ -0,0 +1,57 @@
+// 拷贝构造函数的调用时机
+// 编译器优化，不会调用拷贝构造函数，而是直接创建一个返回值的引用
+#include <iostream>
+
+using namespace std;
+
+class A
+{
+public:
+    int x = 0;
+
+public:
+    A()
+    {
+        cout << this << "  A()" << endl;
+    }
+    A(const A &other)
+    {
+        this->x = other.x;
+        cout << this << "  A(const A &other)" << endl;
+    }
+    ~A()
+    {
+        cout << this << "  ~A()" << endl;
+    }
+};
+
+void test1(A a) // ？是否调用拷贝构造函数
+{
+    cout << "test1(A a) a.x = " << a.x << endl;
+
+    // 当函数结束时，a 释放，会调用析构函数
+}
+
+A test2()
+{
+    A a1; // 局部的类对象， 没有执行拷贝构造函数
+    a1.x = 1;
+    cout << "test2() a1.x = " << a1.x << endl;
+    return a1; // 释放局部对象 a1
+}
+
+void test3()
+{
+    A a2 = test2(); // 返回 A 类的对象，没有调用拷贝构造函数，只是创建了一个 test2() 返回值的引用
+    cout << "test3() a2.x = " << a2.x << endl;
+}
+
+int main()
+{
+    A a0;
+    // test1(a0); // 作为值传递，调用拷贝构造函数
+
+    test3();
+    cout << "over" << endl;
+    return 0;
+}
diff --git a/day3/d7.cpp b/day3/d7.cpp
new file mode 100644
index 0000000..096bf16
--- /dev/null
+++ b/day3/d7.cpp
@@ -0,0 +1,60 @@
+// 拷贝构造函数的调用时机
+// 编译器优化，不会调用拷贝构造函数，而是直接创建一个返回值的引用
+#include <iostream>
+
+using namespace std;
+
+class A
+{
+public:
+    int x = 0;
+
+public:
+    A()
+    {
+        cout << this << "  A()" << endl;
+    }
+    A(const A &other)
+    {
+        this->x = other.x;
+        cout << this << "  A(const A &other)" << endl;
+    }
+    ~A()
+    {
+        cout << this << "  ~A()" << endl;
+    }
+};
+
+void test1(A &a) // ？是否调用拷贝构造函数
+// void test1(A a) // ？是否调用拷贝构造函数
+{
+    cout << "test1(A a) a.x = " << a.x << endl;
+
+    // 当函数结束时，a 释放，会调用析构函数
+}
+
+A test2() // 不要声明为 A &test2(), 因为返回对象时，会释放局部对象，导致返回的引用指向一个已经释放的对象
+{
+    A a1; // 局部的类对象， 没有执行拷贝构造函数
+    a1.x = 1;
+    cout << "test2() a1.x = " << a1.x << endl;
+    return a1; // 释放局部对象 a1
+}
+
+void test3()
+{
+    cout << "tsss = " << endl;
+
+    A a2 = test2(); // 返回 A 类的对象，没有调用拷贝构造函数，只是创建了一个 test2() 返回值的引用
+    cout << "test3() a2.x = " << a2.x << endl;
+}
+
+int main()
+{
+    A a0;
+    test1(a0); // 作为值传递，调用拷贝构造函数
+
+    // test3();
+    cout << "over" << endl;
+    return 0;
+}
diff --git a/day3/d8.cpp b/day3/d8.cpp
new file mode 100644
index 0000000..2faf12b
--- /dev/null
+++ b/day3/d8.cpp
@@ -0,0 +1,30 @@
+// 构造函数的调用规则
+#include <iostream>
+
+using namespace std;
+
+class A
+{
+public:
+    int x, y;
+    void show()
+    {
+        cout << this << " x = " << x << ", y = " << y << endl;
+    }
+};
+
+int main()
+{
+    A a1;
+    // A a2 = a1; // 自动调用拷贝构造函数 A(const A&obj)
+
+    a1.x = 20;
+    A a2 = a1; // 自动调用拷贝构造函数 A(const A&obj)
+
+    a1.y = 30;
+    // A a2 = a1; // 自动调用拷贝构造函数 A(const A&obj)
+
+    a1.show(); // 20,30 浅拷贝
+    a2.show(); //
+    return 0;
+}
diff --git a/day3/d9.cpp b/day3/d9.cpp
new file mode 100644
index 0000000..7e8bcf1
--- /dev/null
+++ b/day3/d9.cpp
@@ -0,0 +1,51 @@
+// 深拷贝和浅拷贝
+// 浅拷贝举例
+#include <iostream>
+#include <cstdlib>
+#include <cstring>
+
+using namespace std;
+
+class Person
+{
+private:
+    char *name;
+    int age;
+
+public:
+    Person(const char *name, int age)
+    {
+        this->name = (char *)malloc(32);
+        this->age = age;
+    }
+    void release_name_pointer()
+    {
+        free(name);
+    }
+
+public:
+    void setName(char *name)
+    {
+        strcpy(this->name, name);
+    }
+    void show()
+    {
+        cout << name << ", " << age << endl;
+    }
+};
+
+int main()
+{
+    Person p1("disen", 20);
+    Person p2 = p1;
+    Person p3 = Person(p2);
+    p3.setName("Jack");
+
+    p1.show();
+    p2.show();
+    p3.show();
+
+    // p1.release_name_pointer();
+    p2.release_name_pointer();
+    return 0;
+}