diff --git a/day9/case1.cpp b/day9/case1.cpp
new file mode 100644
index 0000000..e2906fd
--- /dev/null
+++ b/day9/case1.cpp
@@ -0,0 +1,54 @@
+// 接收一个数值数组，实现数组中元素值从小到大排序
+// 例如：输入 3 2 1 5 4
+// 输出 1 2 3 4 5
+#include <iostream>
+
+using namespace std;
+
+void show(int arr[], int size)
+{
+    int i = 0;
+    while (i < size)
+    {
+        cout << arr[i] << "\t";
+        i++;
+    }
+    cout << endl;
+}
+
+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])
+            {
+                arr[j] = arr[j] ^ arr[j + 1];
+                arr[j + 1] = arr[j] ^ arr[j + 1];
+                arr[j] = arr[j] ^ arr[j + 1];
+            }
+        }
+    }
+}
+
+int main()
+{
+    // 从键盘输入 5 个数值
+    int arr[5];
+    for (int i = 0; i < 5; i++)
+    {
+        cout << "请输入第" << i + 1 << "个数：";
+        cin >> arr[i];
+    }
+    cout << endl;
+
+    cout << "排序前：" << endl;
+    show(arr, 5);
+
+    sort(arr, 5);
+    cout << "排序后：" << endl;
+    show(arr, 5);
+
+    return 0;
+}
\ No newline at end of file
diff --git a/day9/case2.cpp b/day9/case2.cpp
new file mode 100644
index 0000000..ec2931f
--- /dev/null
+++ b/day9/case2.cpp
@@ -0,0 +1,28 @@
+// 接收一个数值数组，对数组中的数值求最大值并输出。
+#include <iostream>
+
+using namespace std;
+
+int maxNum(int arr[], int size)
+{
+    int max = arr[0];
+
+    while (--size)
+    {
+        if (arr[size] > max)
+        {
+            max = arr[size];
+        }
+    }
+
+    return max;
+}
+
+int main()
+{
+    int arr[] = {18, 2, 3, 9, 5, 7}; // 完全初始化
+    int max = maxNum(arr, sizeof(arr) / sizeof(arr[0]));
+    cout << "最大值是: " << max << endl;
+
+    return 0;
+}
\ No newline at end of file
diff --git a/day9/case4.cpp b/day9/case4.cpp
new file mode 100644
index 0000000..04565a2
--- /dev/null
+++ b/day9/case4.cpp
@@ -0,0 +1,32 @@
+// 定义函数, 实现字符串中指定位置字符删除
+#include <iostream>
+
+using namespace std;
+
+void delChar(char str[], int index)
+{
+    int i = index;
+    while (str[i] != '\0')
+    {
+        str[i] = str[i + 1];
+        i++;
+    }
+}
+
+int main()
+{
+    char str[] = "abcdefg";
+    int index;
+    cout << "原字符串: " << str << endl;
+    cout << "请输入要删除的位置: ";
+    cin >> index;
+    if (index < 0 || index > sizeof(str) / sizeof(str[0]))
+    {
+        cout << "位置不合法" << endl;
+        return 0;
+    }
+    delChar(str, index);
+    cout << "删除后: " << str << endl;
+
+    return 0;
+}
\ No newline at end of file
diff --git a/day9/case5.cpp b/day9/case5.cpp
index 41a297e..16bc940 100644
--- a/day9/case5.cpp
+++ b/day9/case5.cpp
@@ -15,7 +15,10 @@ int findCharAt(char str[], int size, char ch)
 
 int main()
 {
-    char str[] = "abcdefg";
+    // char str[] = "abcdefg";
+    char str[128];
+    cout << "请输入字符串: ";
+    cin >> str;
     char ch;
     cout << "请输入要查找的字符: ";
     cin >> ch;
diff --git a/day9/d1.cpp b/day9/d1.cpp
new file mode 100644
index 0000000..2012d25
--- /dev/null
+++ b/day9/d1.cpp
@@ -0,0 +1,25 @@
+// 实现2个整数之和并返回的功能
+#include <iostream>
+
+using namespace std;
+
+// 1. 定义函数
+// a, b是形参
+// addNums是函数名
+int addNums(int a, int b)
+{
+    return a + b;
+}
+
+int main()
+{
+    int x, y;
+    cout << "请输入两个整数：";
+    cin >> x >> y;
+
+    // 2. 调用函数
+    // [变量 = ] 函数名(实参列表);
+    int ret = addNums(x, y); // x, y 是实际变量的数据， 称之为实参
+    cout << "两个整数之和为：" << ret << endl;
+    return 0;
+}
\ No newline at end of file
diff --git a/day9/d2.cpp b/day9/d2.cpp
new file mode 100644
index 0000000..2b70de4
--- /dev/null
+++ b/day9/d2.cpp
@@ -0,0 +1,25 @@
+// 函数的声明
+#include <iostream>
+
+using namespace std;
+
+// 函数的声明
+int addNums(int a, int b);
+
+int main()
+{
+    int x, y;
+    cout << "请输入两个整数：";
+    cin >> x >> y;
+
+    // 2. 调用函数
+    int ret = addNums(x, y); // x, y 是实际变量的数据， 称之为实参
+    cout << "两个整数之和为：" << ret << endl;
+    return 0;
+}
+
+// 函数的定义
+int addNums(int a, int b)
+{
+    return a + b;
+}
\ No newline at end of file
diff --git a/day9/d3.cpp b/day9/d3.cpp
new file mode 100644
index 0000000..dce0dee
--- /dev/null
+++ b/day9/d3.cpp
@@ -0,0 +1,30 @@
+// 有效循环n次，则addNums调用n次，每一次调用都会入栈（创建栈帧）。
+#include <iostream>
+
+using namespace std;
+
+int addNums(int a, int b); // 函数的声明
+
+int main()
+{
+    int x, y;
+    while (1)
+    {
+        cout << "请输入两个整数：";
+        cin >> x;
+        if (x == 0)
+            break;
+        cin >> y;
+        // 调用函数
+        int ret = addNums(x, y);
+        cout << "计算结果为：" << ret << endl;
+    }
+
+    return 0;
+}
+
+// 函数的定义
+int addNums(int a, int b)
+{
+    return a + b;
+}
\ No newline at end of file
diff --git a/day9/d4.cpp b/day9/d4.cpp
new file mode 100644
index 0000000..92d8b2f
--- /dev/null
+++ b/day9/d4.cpp
@@ -0,0 +1,24 @@
+// 判断给定的整数是否为偶数
+#include <iostream>
+
+using namespace std;
+
+int isEven(int n)
+{
+    if (n % 2 == 0)
+        return 1;
+    return 0;
+}
+
+int main()
+{
+    int n;
+    cout << "请输入一个整数：";
+    cin >> n;
+    if (isEven(n))
+        cout << "是偶数" << endl;
+    else
+        cout << "不是偶数" << endl;
+
+    return 0;
+}
\ No newline at end of file
diff --git a/day9/d4_2.cpp b/day9/d4_2.cpp
new file mode 100644
index 0000000..970fe71
--- /dev/null
+++ b/day9/d4_2.cpp
@@ -0,0 +1,24 @@
+// 判断给定的整数是否为偶数
+#include <iostream>
+
+using namespace std;
+
+int isEven(int *n)
+{
+    if (*n % 2 == 0)
+        return 1;
+    return 0;
+}
+
+int main()
+{
+    int n;
+    cout << "请输入一个整数：";
+    cin >> n;
+    if (isEven(&n))
+        cout << "是偶数" << endl;
+    else
+        cout << "不是偶数" << endl;
+
+    return 0;
+}
\ No newline at end of file
diff --git a/day9/d5.cpp b/day9/d5.cpp
new file mode 100644
index 0000000..36c17c7
--- /dev/null
+++ b/day9/d5.cpp
@@ -0,0 +1,51 @@
+
+// 定义函数，接收一个数组和一个整数，从数组中查找到第一个比给定的整数大的数的位置且返回。
+#include <iostream>
+
+using namespace std;
+
+void show(int arr[], int size)
+{
+    int i = 0;
+    while (i < size)
+    {
+        cout << arr[i] << " ";
+        i++
+    }
+    cout << endl;
+}
+
+// arr[] 是 int 类型的一维数组, 此形参准备从外部接收一个 int[] 类型的数组的首地址
+int find(int arr[], int n, int size)
+{
+    for (int i = 0; i < size; i++)
+    {
+        if (arr[i] > n)
+            return i; // 结束循环、结束函数并返回 i
+    }
+
+    return -1;
+}
+
+int main()
+{
+    int arr[] = {1, 2, 3, 0, 5, 7}; // 完全初始化
+    // [注意] 计算数组的长度, 在定义数组的区域可以计算, 如果作为参数传递, 就无法计算了
+    // 这是因为数组作为参数传递时, 会退化为指针, 无法计算长度;
+    // 如果改为指针, 就可以计算长度了, 但是指针无法初始化, 所以必须在定义时初始化
+    int len = sizeof(arr) / sizeof(arr[0]);
+
+    cout << "--- main() ---" << endl;
+    show(arr, len);
+    int n = 0;
+    cout << "查找的数：";
+    cin >> n;
+
+    int index = find(arr, n, len);
+    if (index == -1)
+        cout << "没有找到" << endl;
+    else
+        cout << "找到了，位置是：" << index << ", 第一个比" << n << "大的数是:" << arr[index] << endl;
+
+    return 0;
+}
\ No newline at end of file