diff --git a/day6/a.out b/day6/a.out
new file mode 100755
index 0000000..8ec30d0
Binary files /dev/null and b/day6/a.out differ
diff --git a/day6/d12.c b/day6/d12.c
new file mode 100644
index 0000000..7d1ed2b
--- /dev/null
+++ b/day6/d12.c
@@ -0,0 +1,19 @@
+#include <stdio.h>
+
+int main()
+{
+    char teacher[] = {'d', 'i', 's', 'e', 'n'};
+    printf("%s\n", teacher); // disen
+    int len = sizeof(teacher);
+    printf("%d\n", len); // 5
+    // for (int i = 0; i < len; i++)
+    // {
+    //     printf("%c", teacher[i]);
+    // }
+    int i = 0;
+    while (i < len)
+    {
+        printf("%c", teacher[i++]);
+    }
+    return 0;
+}
\ No newline at end of file
diff --git a/day6/d13.c b/day6/d13.c
new file mode 100644
index 0000000..417db80
--- /dev/null
+++ b/day6/d13.c
@@ -0,0 +1,18 @@
+#include <stdio.h>
+#include <string.h>
+
+int main()
+{
+    char ask_name[32] = "Jack"; // 结果是 "Jack\0"
+    printf("%s\n", ask_name);
+    // sizeof() 统计变量或数组实际分配的内存空间大小，单位是字节
+    printf("ask_name size is %ldB\n", sizeof(ask_name));
+    // strlen() 函数统计有效的字符个数，不包括 '\0' (遇到第一个 '\0' 就停止统计 )
+    printf("ask_name char len is %ld\n", strlen(ask_name));
+
+    char q_what1[128] = "hi,xiao hua\0,love you!";
+    printf("%s\n", q_what1);
+    printf("%ld \n", strlen(q_what1));
+
+    return 0;
+}
\ No newline at end of file
diff --git a/day6/d14.c b/day6/d14.c
new file mode 100644
index 0000000..f0ca0a1
--- /dev/null
+++ b/day6/d14.c
@@ -0,0 +1,23 @@
+#include <stdio.h>
+
+int main()
+{
+    char arr[64] = "hi, disen!";
+    // 实现 strlen() 的功能, 统计字符串的长度
+    int i = 0;
+    while (arr[i])
+        i++;
+    printf("%s length: %d\n", arr, i);
+
+    // 反转字符串
+    int j = 0;
+    int mid = i >> 1; // 含义: i / 2, 位运算更快
+    while (j < mid)
+    {
+        arr[j] ^= arr[i - j - 1];
+        arr[i - j - 1] ^= arr[j];
+        arr[j] ^= arr[i - j - 1];
+        j++;
+    }
+    printf("%s\n", arr);
+}
\ No newline at end of file
diff --git a/day6/d15.c b/day6/d15.c
new file mode 100644
index 0000000..ded73fb
--- /dev/null
+++ b/day6/d15.c
@@ -0,0 +1,20 @@
+#include <stdio.h>
+#include <string.h>
+
+int main()
+{
+    char cmd[32] = "";
+    printf("请输入一个命令：");
+    // scanf() 输入字符串是，遇到第一个空格就停止输入
+    // scanf("%s", cmd); // cmd 数组传递的是地址, 不需要加 & 取地址符
+
+    fgets(cmd, sizeof(cmd), stdin); // 读取一行字符串，遇到回车就停止输入
+    // fgets() 获取的字符最后一个是 '\n' 换行符
+    cmd[strlen(cmd) - 1] = 0; // 将最后一个字符 '\n' 换成 '\0' 空字符
+
+    // printf("%s \n", cmd);
+    // for (int i = 0; i < 32; i++)
+    printf("%s, %ld\n", cmd, strlen(cmd));
+    printf("\n");
+    return 0;
+}
\ No newline at end of file
diff --git a/day6/d17.c b/day6/d17.c
new file mode 100644
index 0000000..1e190a4
--- /dev/null
+++ b/day6/d17.c
@@ -0,0 +1,25 @@
+#include <stdio.h>
+#include <string.h>
+
+int main()
+{
+    // char stu_names[5][32] = {"zhangsan", "lisi", "wangwu", "zhaoliu", "tianqi"};
+    char stu_names[5][32];
+    int i = 0;
+    while (i < 5)
+    {
+        printf("请输入第 %d 个学生的名字：", i + 1);
+        fgets(stu_names[i], sizeof(stu_names[i]), stdin);
+
+        stu_names[i][strlen(stu_names[i]) - 1] = '\0';
+
+        i++;
+    }
+
+    for (int i = 0; i < 5; i++)
+    {
+        printf("%s\n", stu_names[i]);
+    }
+
+    return 0;
+}
\ No newline at end of file
diff --git a/day6/d18.c b/day6/d18.c
new file mode 100644
index 0000000..a2da580
--- /dev/null
+++ b/day6/d18.c
@@ -0,0 +1,2 @@
+#include <stdio.h>
+#include <string.h>
diff --git a/day6/d19.c b/day6/d19.c
new file mode 100644
index 0000000..cf7fbaa
--- /dev/null
+++ b/day6/d19.c
@@ -0,0 +1,6 @@
+#include <stdio.h>
+#include <string.h>
+
+int main()
+{
+}
\ No newline at end of file
diff --git a/day6/d6.c b/day6/d6.c
new file mode 100644
index 0000000..dba1dce
--- /dev/null
+++ b/day6/d6.c
@@ -0,0 +1,33 @@
+#include <stdio.h>
+
+int main()
+{
+    int nums[5][3] = {0};
+    int n;
+    for (int i = 0; i < 5; i++)
+    {
+        printf("请输入第%d个三位数：", i + 1);
+        scanf("%d", &n);
+
+        int m[] = {100, 10, 1};
+        int j = 0;
+        while (n > 0)
+        {
+            nums[i][j] = n / m[j];
+            n %= m[j];
+            j++;
+        }
+    }
+
+    for (int i = 0; i < 5; i++)
+    {
+        // 判断这个三位数是否为回文数
+        if (nums[i][0] == nums[i][2])
+            continue;
+        for (int j = 0; j < 3; j++)
+        {
+            printf("%d ", nums[i][j]);
+        }
+        printf("\n");
+    }
+}