diff --git a/README.md b/README.md
index 2655caf..794b4d3 100644
--- a/README.md
+++ b/README.md
@@ -3,3 +3,5 @@
 # 千锋 C++阶段
 
 #### 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
diff --git a/day2/ce1.cpp b/day2/ce1.cpp
new file mode 100644
index 0000000..cb5573b
--- /dev/null
+++ b/day2/ce1.cpp
@@ -0,0 +1,78 @@
+// Classroom exercises: 课堂练习
+// ce
+// 类的定义和使用
+#include <iostream>
+#include <cstring>
+
+using namespace std;
+
+class Person
+{
+public:
+    void init(const char *iname, int iage);
+    void setName(const char sname[]);
+    void setAge(int sage);
+    const char *getname();
+    const int getAge();
+    const void show();
+
+private:
+    char name[32];
+    int age;
+};
+
+void Person::init(const char *iname, int iage)
+{
+    strcpy(this->name, iname);
+    if (iage > 0 && iage < 100)
+        this->age = iage;
+    else
+    {
+        this->age = 0;
+        cout << "年龄超出范围，拒绝赋值!" << endl;
+    }
+}
+
+void Person::setName(const char sname[])
+{
+    strcpy(this->name, sname);
+}
+
+void Person::setAge(int sage)
+{
+    if (sage > 0 && sage < 100)
+        this->age = sage;
+    else
+    {
+        cout << "年龄超出范围，拒绝赋值!" << endl;
+    }
+}
+
+const char *Person::getname()
+{
+    return this->name;
+}
+
+const int Person::getAge()
+{
+    return this->age;
+}
+
+const void Person::show()
+{
+    cout << "name = " << this->name << ", age = " << this->age << endl;
+}
+
+int main()
+{
+    Person p1;
+    p1.setAge(20);
+    p1.setName("flykhan");
+    p1.show();
+
+    Person p2;
+    p2.init("hello", 0);
+    p2.show();
+
+    return 0;
+}
diff --git a/day2/d1.cpp b/day2/d1.cpp
new file mode 100644
index 0000000..0ddc71b
--- /dev/null
+++ b/day2/d1.cpp
@@ -0,0 +1,30 @@
+// 引用的使用
+// 引用的本质是指针常量，所以引用的空间大小和指针相同，都是 8 个字节
+// 引用的本质是指针常量，所以引用的指向不能改变，但是指向的值可以改变
+// 引用的本质是指针常量，所以引用在定义时必须初始化，且不能再引用其他变量
+// int a = 10;
+// int &aa = a; // int * const aa = &a;
+#include <iostream>
+
+using namespace std;
+
+int main()
+{
+    // 定义引用时，必须给初始化值，另外，定义之后引用不能再引用其他变量
+    int a = 10;
+    int &b = a; // 对 a 的引用
+    b += 20;    // 相当于 a += 20
+    cout << "a: " << a << " b: " << b << endl;
+
+    int &c = a;
+    cout << "a: " << a << " b: " << b << " c: " << c << endl;
+
+    int &d = b;
+    cout << "a: " << a << " b: " << b << " c: " << c << " d: " << d << endl;
+
+    int x = 100;
+    c = x;
+    cout << "c: " << c << endl;
+
+    return 0;
+}
diff --git a/day2/d10.cpp b/day2/d10.cpp
new file mode 100644
index 0000000..9aec061
--- /dev/null
+++ b/day2/d10.cpp
@@ -0,0 +1,30 @@
+#include <iostream>
+
+using namespace std;
+
+void f(int a, int)
+{
+    cout << "f(int, int )" << endl;
+}
+
+void f(double, int)
+{
+    cout << "f(double, int)" << endl;
+}
+
+void f(int a)
+{
+    cout << "f(int)" << endl;
+}
+
+void f(double a)
+{
+    cout << "f(double)" << endl;
+}
+
+int main()
+{
+    f(1);
+    f(1.0, 2);
+    return 0;
+}
diff --git a/day2/d11/area.c b/day2/d11/area.c
new file mode 100644
index 0000000..beb818a
--- /dev/null
+++ b/day2/d11/area.c
@@ -0,0 +1,6 @@
+#include "area.h"
+
+double S(double r)
+{
+    return r * r * 3.1415926;
+}
\ No newline at end of file
diff --git a/day2/d11/area.h b/day2/d11/area.h
new file mode 100644
index 0000000..9f2db4f
--- /dev/null
+++ b/day2/d11/area.h
@@ -0,0 +1,15 @@
+#ifndef __AREA_H__
+#define __AREA_H__
+
+// 条件编译
+#if __cplusplus
+extern "C"
+{
+#endif
+    double S(double r);
+
+#if __cplusplus
+}
+#endif
+
+#endif
\ No newline at end of file
diff --git a/day2/d11/main.cpp b/day2/d11/main.cpp
new file mode 100644
index 0000000..4f45d42
--- /dev/null
+++ b/day2/d11/main.cpp
@@ -0,0 +1,12 @@
+#include <iostream>
+#include "area.h"
+
+using namespace std;
+
+int main()
+{
+    double r = 2.5;
+    double s = S(r);
+    cout << "S(2.5) = " << s << endl;
+    return 0;
+}
diff --git a/day2/d12.cpp b/day2/d12.cpp
new file mode 100644
index 0000000..82c9661
--- /dev/null
+++ b/day2/d12.cpp
@@ -0,0 +1,26 @@
+#include <iostream>
+
+using namespace std;
+
+// 增强的结构体（c 中结构体中只有变量）
+struct Person
+{
+    int pid;
+    int age;
+    void show() // C++ 的结构体中可以加函数
+    {
+        // 可以访问同一结构体内的成员变量
+        cout << "pid = " << pid << ", age = " << age << endl;
+    }
+};
+
+int main()
+{
+    Person p1 = {1001, 21};
+    p1.show();
+
+    Person p2 = {1002, 19};
+    p2.show();
+
+    return 0;
+}
diff --git a/day2/d13.cpp b/day2/d13.cpp
new file mode 100644
index 0000000..b474d39
--- /dev/null
+++ b/day2/d13.cpp
@@ -0,0 +1,44 @@
+// 类
+#include <iostream>
+#include <cstring>
+using namespace std;
+
+namespace SA
+{
+    class Student
+    {
+    public:
+        int sid = 14; // 默认值设定，需要 c++11 标准以上
+        char name[32] = "hello";
+
+    private:
+        float score = 90;
+
+    public:
+        void showScore(); // 声明类方法
+        void addScore(float n) { this->score = n; }
+    };
+
+    // 实现类中的方法（函数）
+    void Student::showScore()
+    {
+        cout << "sid = " << this->sid << ", name = " << this->name << ", score = " << this->score << endl;
+    }
+};
+
+using namespace SA;
+
+int main()
+{
+
+    Student s1;
+    strcpy(s1.name, "flykhan");
+    s1.sid = 1001;
+    s1.addScore(100);
+    s1.showScore();
+
+    Student s2;
+    s2.showScore();
+
+    return 0;
+}
diff --git a/day2/d14.cpp b/day2/d14.cpp
new file mode 100644
index 0000000..56a1c64
--- /dev/null
+++ b/day2/d14.cpp
@@ -0,0 +1,81 @@
+// 立方体类与应用
+#include <iostream>
+
+using namespace std;
+
+class Cube
+{
+public:
+    void init(int l, int w, int h)
+    {
+        this->a = l;
+        this->b = w;
+        this->c = h;
+    }
+    int S(); // 面积
+    int V(); // 体积
+    void show();
+    bool isEqual(Cube &tmp);
+
+private:
+    int a; // 长
+    int b; // 宽
+    int c; // 高
+};
+
+int Cube::S()
+{
+    return 2 * (a * b + a * c + b * c);
+}
+
+int Cube::V()
+{
+    return a * b * c;
+}
+
+void Cube::show()
+{
+    cout << "S = " << S() << ", V = " << V() << endl;
+}
+
+bool Cube::isEqual(Cube &tmp)
+{
+    // if (this->a == tmp.a && this->b == tmp.b && this->c == tmp.c)
+    if (this->S() == tmp.S() && this->V() == tmp.V())
+        return true;
+    else
+        return false;
+}
+
+bool equalCube(Cube &c1, Cube &c2)
+{
+    if (c1.S() == c2.S() && c1.V() == c2.V())
+        return true;
+    return false;
+}
+
+const char *resBool(bool b) // bool 数字值转换人类可读
+{
+    if (b != 0)
+        return "true";
+    return "false";
+}
+
+int main()
+{
+    Cube c1, c2, c3;
+    c1.init(2, 3, 4);
+    cout << "c1: " << endl;
+    c1.show();
+
+    c2.init(3, 4, 5);
+    cout << "c2: " << endl;
+    c2.show();
+
+    c3.init(4, 2, 3);
+
+    cout << "Cube::isEqual(c2) = " << resBool(c1.isEqual(c2)) << endl;
+    cout << "equalCube(c1, c2) = " << resBool(equalCube(c1, c3)) << endl;
+
+    return 0;
+}
diff --git a/day2/d15.cpp b/day2/d15.cpp
new file mode 100644
index 0000000..f0959a5
--- /dev/null
+++ b/day2/d15.cpp
@@ -0,0 +1,83 @@
+// 点和圆的关系
+#include <iostream>
+#include <cmath>
+
+using namespace std;
+
+enum Pos_e
+{
+    onCircle = 4, // 点在圆上
+    inCircle,     // 点在圆内
+    outCircle     // 点在圆外
+};
+
+class Point
+{
+public:
+    int x, y;
+};
+
+class AdvCircle
+{
+public:
+    int init(int x0, int y0, int r)
+    {
+        this->r = r;
+        o.x = x0;
+        o.y = y0;
+    }
+
+    Pos_e at(Point &point);
+
+private:
+    int r;
+    Point o; // 圆心点
+};
+
+Pos_e AdvCircle::at(Point &point)
+{
+    int distence = pow((point.x - this->o.x), 2) + pow((point.y - this->o.y), 2);
+    int rr = r * r;
+    if (distence == rr)
+    {
+        return onCircle;
+    }
+    else if (distence < rr)
+    {
+        return inCircle;
+    }
+    else
+        return outCircle;
+}
+
+string posToString(Pos_e pos)
+{
+    switch (pos)
+    {
+    case onCircle:
+        return "在圆上";
+        break;
+    case inCircle:
+        return "在圆内";
+        break;
+    case outCircle:
+        return "在圆外";
+        break;
+    default:
+        break;
+    }
+}
+
+int main()
+{
+    AdvCircle c1;
+    c1.init(0, 0, 2);
+
+    Point p1;
+    p1.x = 1;
+    p1.y = 1;
+
+    cout << "c1.at(p1) " << posToString(c1.at(p1)) << endl;
+
+    return 0;
+}
diff --git a/day2/d2.cpp b/day2/d2.cpp
new file mode 100644
index 0000000..93fe286
--- /dev/null
+++ b/day2/d2.cpp
@@ -0,0 +1,23 @@
+// 引用相当于变量的别名
+#include <iostream>
+
+using namespace std;
+
+int main()
+{
+    int arr[5] = {1, 2, 3, 4, 5};
+
+    // 给 arr 设置一个别名(引用)
+    // 先定义 5 个元素数组类型的别名
+    typedef int ArrRef[5];
+    ArrRef &a = arr;
+
+    // 通过别名操作数组
+    for (int i = 0; i < 5; i++)
+    {
+        cout << a[i] << " ";
+    }
+    cout << endl;
+
+    return 0;
+}
diff --git a/day2/d2_2.cpp b/day2/d2_2.cpp
new file mode 100644
index 0000000..61a958e
--- /dev/null
+++ b/day2/d2_2.cpp
@@ -0,0 +1,21 @@
+// 数组引用的方法二
+#include <iostream>
+
+using namespace std;
+
+int main()
+{
+    int arr[5] = {1, 2, 3, 4, 5};
+
+    // 直接定义 5 个元素数组类型的引用
+    int(&a)[5] = arr;
+
+    // 通过别名操作数组
+    for (int i = 0; i < 5; i++)
+    {
+        cout << a[i] << " ";
+    }
+    cout << endl;
+
+    return 0;
+}
diff --git a/day2/d3.cpp b/day2/d3.cpp
new file mode 100644
index 0000000..7371f14
--- /dev/null
+++ b/day2/d3.cpp
@@ -0,0 +1,23 @@
+#include <iostream>
+
+using namespace std;
+
+// 引用传递: 会改变实参的值
+// 值传递: 不会改变实参的值
+void cumsum(int &total, int n) // total 是引用传递，n 是值传递
+{
+    total += n;
+}
+
+int main()
+{
+    int total = 0;
+    int n = 0;
+    while (cin >> n)
+    {
+        cumsum(total, n);
+        cout << "total = " << total << endl;
+        if (total > 100)
+            break;
+    }
+}
\ No newline at end of file
diff --git a/day2/d4.cpp b/day2/d4.cpp
new file mode 100644
index 0000000..add5246
--- /dev/null
+++ b/day2/d4.cpp
@@ -0,0 +1,28 @@
+#include <iostream>
+#define N 10 // 定义常量
+
+using namespace std;
+
+typedef int TenArr[N];
+
+TenArr &new_arr()
+{
+    static int m[N] = {0}; // 全局静态区存储，程序结束后才释放
+    for (int i = 0; i < N; i++)
+    {
+        m[i] = i;
+    }
+    return m;
+}
+
+int main()
+{
+    TenArr &p = new_arr();
+    int i = 0;
+    while (i < N)
+    {
+        cout << "p[" << i << "] = " << p[i++] << endl;
+    }
+
+    return 0;
+}
diff --git a/day2/d5.cpp b/day2/d5.cpp
new file mode 100644
index 0000000..8f2cda1
--- /dev/null
+++ b/day2/d5.cpp
@@ -0,0 +1,57 @@
+#include <iostream>
+
+#define N 7
+
+using namespace std;
+
+void sort(int (&arr)[N])
+{
+    for (int i = 0; i <= N - 1; i++)
+    {
+        for (int j = 0; j <= N - i - 1; j++)
+        {
+            if (arr[j] > arr[j + 1])
+            {
+                arr[j] ^= arr[j + 1];
+                arr[j + 1] ^= arr[j];
+                arr[j] ^= arr[j + 1];
+                // int temp = arr[j];
+                // arr[j] = arr[j + 1];
+                // arr[j + 1] = temp;
+            }
+        }
+    }
+}
+
+void sort(int arr[], int size)
+{
+    for (int i = 0; i < size - 1; i++)
+    {
+        for (int j = 0; j < size - i - 1; j++)
+        {
+            if (arr[j] > arr[j + 1])
+            {
+                int temp = arr[j];
+                arr[j] = arr[j + 1];
+                arr[j + 1] = temp;
+            }
+        }
+    }
+}
+
+int main()
+{
+    int nums[] = {1, 5, 2, 0, 9, 10, 7};
+    int size = sizeof(nums) / sizeof(nums[0]);
+
+    sort(nums);
+    // sort(nums, size);
+
+    for (int i = 0; i < size; i++)
+    {
+        cout << nums[i] << "\t";
+    }
+    cout << endl;
+
+    return 0;
+}
diff --git a/day2/d6.cpp b/day2/d6.cpp
new file mode 100644
index 0000000..3c7afa7
--- /dev/null
+++ b/day2/d6.cpp
@@ -0,0 +1,29 @@
+// 指针的引用
+// 为指针取个别名，相当于'指针的指针'
+#include <iostream>
+#include <cstdlib>
+
+using namespace std;
+
+struct STU
+{
+    int sid;
+    float score;
+};
+
+void set_score(STU *&q, int sid, float score)
+{
+    q->sid = sid;
+    q->score = score;
+}
+
+int main()
+{
+    STU *p = (STU *)malloc(sizeof(STU));
+
+    set_score(p, 1, 99);
+
+    cout << "sid = " << p->sid << ", score = " << p->score << endl;
+
+    return 0;
+}
diff --git a/day2/d6_2.cpp b/day2/d6_2.cpp
new file mode 100644
index 0000000..4c83117
--- /dev/null
+++ b/day2/d6_2.cpp
@@ -0,0 +1,30 @@
+// 指针的引用
+// 为指针取个别名，相当于'指针的指针'
+#include <iostream>
+#include <cstdlib>
+
+using namespace std;
+
+struct STU
+{
+    int sid;
+    float score;
+};
+
+// 指针的指针
+void set_score(STU **q, int sid, float score)
+{
+    (*q)->sid = sid;
+    (*q)->score = score;
+}
+
+int main()
+{
+    STU *p = (STU *)malloc(sizeof(STU));
+
+    set_score(&p, 2, 98);
+
+    cout << "sid = " << p->sid << ", score = " << p->score << endl;
+
+    return 0;
+}
diff --git a/day2/d7.cpp b/day2/d7.cpp
new file mode 100644
index 0000000..d96b1fa
--- /dev/null
+++ b/day2/d7.cpp
@@ -0,0 +1,28 @@
+// 常量引用
+// 相当于 常量指针常量
+// 用法: const 数据类型 &变量名 = 其他变量或常量
+
+// 注意:
+// 一般的引用不能赋值常量（字面量），但是 const 引用可以赋值常量
+#include <iostream>
+
+using namespace std;
+
+int main()
+{
+
+    int x = 10;
+    const int &x1 = x;
+
+    // error: assignment of read - only reference ‘x1’
+    x1 -= 5; // const 修饰的引用不能修改内容
+    cout << "x = " << x << endl;
+
+    const int &x2 = 50;
+    cout << "x2 = " << x2 << endl;
+
+    // error: invalid initialization of non-const reference of type ‘int&’ from an rvalue of type ‘int’
+    int &x3 = 'a'; // 常量不能赋值给非常量引用
+    cout << "x3 = " << x3 << endl;
+    return 0;
+}
diff --git a/day2/d8.cpp b/day2/d8.cpp
new file mode 100644
index 0000000..5d7775b
--- /dev/null
+++ b/day2/d8.cpp
@@ -0,0 +1,26 @@
+// 内联函数
+// 函数前面添加了 inline 关键字，则此函数为内联函数
+// 内联函数只能在当前文件中使用，相当于函数前面加 static
+
+// 内联函数一般用于替换 有参的宏，有参宏经常会出错，而且参数是无数据类型
+// 每一次使用内联函数时，都会像有参宏一样，展开一次（内联函数不入栈，运行效率高，编译时会提前处理）
+#include <iostream>
+
+using namespace std;
+
+#define ADD(x, y) x + y
+// 内联函数
+inline int add(int a, int b)
+{
+    return a + b;
+}
+
+int main()
+{
+    int ret1 = ADD(10, 20) * 10;
+    cout << "ret = " << ret1 << endl;
+
+    int ret2 = add(10, 20) * 10;
+    cout << "ret = " << ret2 << endl;
+    return 0;
+}
diff --git a/day2/d9.cpp b/day2/d9.cpp
new file mode 100644
index 0000000..a5d286f
--- /dev/null
+++ b/day2/d9.cpp
@@ -0,0 +1,30 @@
+// 函数的默认参数
+
+#include <iostream>
+
+using namespace std;
+
+bool isSs(int n = 10) // 判断 n 是否为质数
+{
+    int i = 2;
+    for (; i < n / 2; i++)
+    {
+        if (n % i == 0)
+            return false; // 0 为假
+    }
+    return true; // 非 0 为真
+}
+
+double area(double r = 1.0) // 求面积
+{
+    return 3.14 * r * r;
+}
+
+int main()
+{
+    cout << "isSS(7) is " << isSs(7) << endl;
+    cout << "isSS() is " << isSs() << endl;
+    cout << "area() is " << area() << endl;
+    cout << "area(2) is " << area(2) << endl;
+    return 0;
+}