From b1c38f25c4218d60308ba0d8d5b5aa748345c358 Mon Sep 17 00:00:00 2001
From: flykhan <liubo666666@outlook.com>
Date: Thu, 15 Jun 2023 15:15:50 +0800
Subject: [PATCH] =?UTF-8?q?=E5=8F=98=E9=87=8F=E7=9A=84=E4=BD=9C=E7=94=A8?=
 =?UTF-8?q?=E5=9F=9F?=
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---
 day4/d5.cpp | 24 ++++++++++++++++++++++++
 day4/d7.cpp | 21 +++++++++++++++++++++
 2 files changed, 45 insertions(+)
 create mode 100644 day4/d5.cpp
 create mode 100644 day4/d7.cpp

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;
+}