diff --git a/【实践课内】9.数组3/7-1 字符串逆序.c b/【实践课内】9.数组3/7-1 字符串逆序.c
new file mode 100644
index 0000000..a6e92f1
--- /dev/null
+++ b/【实践课内】9.数组3/7-1 字符串逆序.c	
@@ -0,0 +1,18 @@
+#include <stdio.h>
+#include <string.h>
+
+char s[100];
+
+int main() {
+    gets(s);
+
+    int len = strlen(s);
+
+    for (int i = len - 1; i >= 0; i--) {
+        printf("%c", s[i]);
+    }
+
+    printf("\n");
+
+    return 0;
+}
diff --git a/【实践课内】9.数组3/7-1 字符串逆序.png b/【实践课内】9.数组3/7-1 字符串逆序.png
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index 0000000..f566043
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diff --git a/【实践课内】9.数组3/7-2 字符串替换.c b/【实践课内】9.数组3/7-2 字符串替换.c
new file mode 100644
index 0000000..b9a77e3
--- /dev/null
+++ b/【实践课内】9.数组3/7-2 字符串替换.c	
@@ -0,0 +1,23 @@
+#include <stdio.h>
+
+const char REPLACE_MAP[] = "ZYXWVUTSRQPONMLKJIHGFEDCBA";
+
+char s[100];
+
+int main() {
+    gets(s);
+
+    int len = strlen(s);
+
+    for (int i = 0; i < len; i++) {
+        if (s[i] >= 'A' && s[i] <= 'Z') {
+            printf("%c", REPLACE_MAP[s[i] - 'A']);
+        } else {
+            printf("%c", s[i]);
+        }
+    }
+
+    printf("\n");
+
+    return 0;
+}
diff --git a/【实践课内】9.数组3/7-2 字符串替换.png b/【实践课内】9.数组3/7-2 字符串替换.png
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index 0000000..9de386c
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diff --git a/【实践课内】9.数组3/7-3 统计字符出现次数.c b/【实践课内】9.数组3/7-3 统计字符出现次数.c
new file mode 100644
index 0000000..0cc248f
--- /dev/null
+++ b/【实践课内】9.数组3/7-3 统计字符出现次数.c	
@@ -0,0 +1,21 @@
+#include <stdio.h>
+
+char c, s[100];
+
+int main() {
+    gets(s);
+    scanf("%c", &c);
+
+    int len = strlen(s);
+    int cnt = 0;
+
+    for (int i = 0; i < len; i++) {
+        if (s[i] == c) {
+            cnt++;
+        }
+    }
+
+    printf("%d\n", cnt);
+
+    return 0;
+}
diff --git a/【实践课内】9.数组3/7-3 统计字符出现次数.png b/【实践课内】9.数组3/7-3 统计字符出现次数.png
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diff --git a/【实践课内】9.数组3/7-4 IP地址转换.c b/【实践课内】9.数组3/7-4 IP地址转换.c
new file mode 100644
index 0000000..970031a
--- /dev/null
+++ b/【实践课内】9.数组3/7-4 IP地址转换.c	
@@ -0,0 +1,18 @@
+#include <stdio.h>
+
+char s[100];
+int ip[4];
+
+int main() {
+    scanf("%s", s);
+
+    for (int i = 0; i < 4; i++) {
+        for (int j = 0; j < 8; j++) {
+            ip[i] = ip[i] * 2 + s[i * 8 + j] - '0';
+        }
+    }
+
+    printf("%d.%d.%d.%d\n", ip[0], ip[1], ip[2], ip[3]);
+
+    return 0;
+}
diff --git a/【实践课内】9.数组3/7-4 IP地址转换.png b/【实践课内】9.数组3/7-4 IP地址转换.png
new file mode 100644
index 0000000..0e05791
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