Difference between revisions of "Practice Everyday"

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 </syntaxhighlight>
+不过，有个小问题，如果是一篇文章，这样从终端输入的方式似乎就不太好，对吧。实用性不高，那读取文件呢？
+<syntaxhighlight lang="c" line style="border: 1px dashed red;">
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+// encrypt
+void encrypt(char *str, int key)
+{
+    int len = strlen(str);
+    for (int i = 0; i < len; i++)
+    {
+        str[i] += key;
+    }
+}
+// decrypt
+void decrypt(char *str, int key)
+{
+    int len = strlen(str);
+    for (int i = 0; i < len; i++)
+    {
+        str[i] -= key;
+    }
+}
+int main()
+{
+    char filename[100];
+    char buffer[1024];
+    int key;
+    // OK, read a file, fancy right?
+    printf("请输入要读取的文件名：");
+    scanf("%s", filename);
+    printf("请输入密钥：");
+    scanf("%d", &key);
+    // let's encrypt what do you want, and, write back result, more fancy, right?
+    // Do you want write a user interface: user choose 'encrypt' or 'decrypt'
+    FILE *fp = fopen(filename, "r");
+    if (fp == NULL)
+    {
+        printf("无法打开文件 %s\n", filename);
+        return 1;
+    }
+    fseek(fp, 0L, SEEK_END); // 定位到文件末尾
+    long size = ftell(fp);   // 获取文件大小
+    fseek(fp, 0L, SEEK_SET); // 定位到文件开头
+    fread(buffer, sizeof(char), size, fp); // 读取整个文件
+    fclose(fp);
+    // do it!
+    encrypt(buffer, key);
+    // Done! cool.
+    fp = fopen(filename, "a");
+    if (fp == NULL)
+    {
+        printf("无法打开文件 %s\n", filename);
+        return 1;
+    }
+    fprintf(fp, "\n\n加密后的内容：\n%s", buffer);
+    fclose(fp);
+    printf("加密完成！\n");
+    return 0;
+}
+</syntaxhighlight>
+感觉不错。但是是不是可以进一步优化一下下？譬如，写几句，让用户选择是加密还是解密，然后呢，再执行加密或解密的算法？这个小玩具够这个周五的晚上玩儿一阵子的了吧，哈哈哈。
 == Day 92 ==