同一文档读写凯撒密码.cpp

可在同一文档里读写凯撒密码

// ks.cpp : Defines the entry point for the console application.
//

#include "stdio.h"
#include "math.h"
int main(int argc, char* argv[])
{
	FILE* fp;
    FILE* fq;
	int n,i;
	char ch,filename[10];
    printf("请输入需要读取的文件:\n");
	scanf("%s",filename);
	printf("密钥:\n");
	scanf("%d",&n);
	if((fp=fopen(filename,"r"))==NULL)
	{
		printf("不能打开此文件\n");
	    //exit(0);
	}
	printf("请输入需要写入的文件:\n");
	scanf("%s",filename);
	if((fq=fopen(filename,"a"))==NULL)
	{
		printf("不能打开此文件\n");
	    //exit(0);
	}
	ch=fgetc(fp);
    while(!feof(fp))
	{
       if(ch>='a'&&ch<='z')
           ch='a'+(ch-'a'+n)%26;
	       
	   else
       {
         if(ch>='A'&&ch<='Z')
           ch='A'+(ch-'A'+n)%26;
       }
       fputc(ch,fq);
       putchar(ch);
       ch=fgetc(fp);
	}
	fclose(fq);
	return 0;
}