c - 如何使用 C 语言中的文件编写凯撒密码加密代码

Question

对于凯撒密码加密，我有这个代码。该程序使用用户编写的文本。但我希望从文本文件中读取它并运行。

#include<stdio.h>
#include <conio.h>
#include<string.h>

void main()
{
  int key,i;
  char [30];
  clrscr();
  printf("\n enter plain text : ");
  gets(data);
  printf("\ enter key value : ");
  scanf("%d",&key);
  {
    for (i=o;i<strlen(data);i++) {
      if (data[i]==' ') {}
      else
      {
        if (data[i]>='x')
        {
          data[i]=data[i]-26;
        }
        data[i]=data[i]+key;
      }
    }
  } 
  printf("your cipher text is : %s",data);
  getch();
}

Answer 1

您刚刚是从某处复制并粘贴此代码吗？

正如其他人已经指出的那样，您的代码存在一些相当大的问题，因此我将尝试讨论他们在整个过程中没有提到的问题。首先，您应该将 main 声明为 int。返回值告诉您程序是否正确退出，这不仅仅是约定。

这是您的原始代码，已格式化。我删除了 conio.h 因为它已被弃用多年，而且您在这里不需要它。它所做的只是为您清除屏幕，您可以使用 System("CLS"); 来完成此操作，尽管 here是一篇很棒的文章，已在 SO 上分享过多次，解释了为什么您应该避免使用它。

#include<stdio.h>
#include<string.h>

int main()
{
  int key,i;

  // original: char [30];
  // I'm guess you copied and pasted wrong?
  char plainText[30];

  printf("\n enter plain text : ");
  gets(data);
  printf("\nenter key value : ");
  scanf("%d",&key);

  // You had brackets here, essentially creating an unnecessary
  // block of code.
  for(i=o;i<strlen(data);i++)
  {
    // Where did the "data" variable come from? You haven't declared it
    // and you're trying to get its length in this for loop
    if (data[i]==' ')
    {
      // ?
    }
  else
    {
      if (data[i]>='x')
      {
          // Instead of this approach I would go with a modulus operation
          // If you're not familiar with modular arithmetic I really recommend you look
          // it up. It's absolutely essential in cryptography. It's central to both
          // symmetric and asymmetric key cryptography.
          data[i]=data[i]-26;
      }

    // This is the heart of the Caesar cipher right here. This is where you're actually
    // shifting the characters, so it's a literal Caesar cipher  
    data[i]=data[i]+key;
    }
  }

  // Again, you haven't declared "data" so you can't call it. I'm guessing you didn't
  // try to compile this program because it is teeming with errors GCC, Clang, and VC++
  // would have caught immediately
  printf("your cipher text is : %s",data);
  getch();

  // Remember to make your "main" function return an <code>int</code>. This value is
  // very important, especially when your program gets called by another program because
  // it's how your program communicates that it ran successfully, or something went
  // wrong. In that case you could set a specific error code to know exactly
  // what went wrong and were

  // Example:
  int x = 1;
  if (x == 1)
      exit(4);

  // This program would now exit with a status of 4, which you would then know was due
  // to this function. This was a contrived example, but hopefully you get the gist
  return 0;
}