diff --git a/day4/d5.cpp b/day4/d5.cpp
new file mode 100644
index 0000000..fb41388
--- /dev/null
+++ b/day4/d5.cpp
@@ -0,0 +1,24 @@
+#include <iostream>
+
+using namespace std;
+
+int n;  // 全局变量
+
+// 定义函数
+void test1()
+{
+    n = 100;
+}
+
+int main()
+{
+    test1(); // 调用 test1 函数
+    cout << "global n = " << n << endl;
+    {
+        int m;
+        cout << "local m = " << m << endl;
+    }
+    // 跳出局部区域 m 变量则不能访问
+    // cout << "m = " << m << endl;
+    return 0;
+}
diff --git a/day4/d7.cpp b/day4/d7.cpp
new file mode 100644
index 0000000..e3b066f
--- /dev/null
+++ b/day4/d7.cpp
@@ -0,0 +1,21 @@
+#include <iostream>
+
+using namespace std;
+
+// 声明变量 n 为 int 类型
+extern int n;
+// void 表示无返回数据
+void test2()
+{
+    // 假如存在一个全局变量 n
+    n += 20; // n=n+20; += 符合赋值运算符
+    cout << "int test2 function n = " << n << endl;
+}
+
+int n = 10;
+int main()
+{
+    test2();
+    cout << "int main function n = " << n << endl;
+    return 0;
+}