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

void menu()/*菜单，1.加密 2.解密 3.退出*/
{
clrscr();
printf("\n===============================================================================");
printf("\n1.Encrypt the file");
printf("\n2.Decrypt the file");
printf("\n3.Quit\n");
printf("===============================================================================\n");
printf("Please select a item:");
return;
}

char encrypt(char ch,int n)/*加密函数，把字符向右循环移位n*/
{
while(ch>='A'&&ch<='Z')
{
return ('A'+(ch-'A'+n)%26);
}
while(ch>='a'&&ch<='z')
{
return ('a'+(ch-'a'+n)%26);
}
return ch;
}


main()
{
int i,n;
char ch0,ch1;
FILE *in,*out;
char infile[10],outfile[10];

textbackground(RED);
textcolor(LIGHTGREEN);
clrscr();

menu();
ch0=getch();

while(ch0!='3')
{
if(ch0=='1')
{
   clrscr();
   printf("\nPlease input the infile:");
   scanf("%s",infile);/*输入需要加密的文件名*/

   if((in=fopen(infile,"r"))==NULL)
   {
    printf("Can not open the infile!\n");
    printf("Press any key to exit!\n");
    getch();
    exit(0);
   }

   printf("Please input the key:");
   scanf("%d",&n);/*输入加密密码*/

   printf("Please input the outfile:");
   scanf("%s",outfile);/*输入加密后文件的文件名*/

   if((out=fopen(outfile,"w"))==NULL)
   {
    printf("Can not open the outfile!\n");
    printf("Press any key to exit!\n");
    fclose(in);
    getch();
    exit(0);
   }

   while(!feof(in))/*加密*/
   {
    fputc(encrypt(fgetc(in),n),out);
   }

   printf("\nEncrypt is over!\n");
   fclose(in);
   fclose(out);
   sleep(1);
}

if(ch0=='2')
{
   clrscr();
                     printf("\nPlease input the infile:");
   scanf("%s",infile);/*输入需要解密的文件名*/

                        if((in=fopen(infile,"r"))==NULL)
   {
    printf("Can not open the infile!\n");
    printf("Press any key to exit!\n");
    getch();
    exit(0);
   }

   printf("Please input the key:");
   scanf("%d",&n);/*输入解密密码（可以为加密时候的密码）*/

   n=26-n;

   printf("Please input the outfile:");
   scanf("%s",outfile);/*输入解密后文件的文件名*/

   if((out=fopen(outfile,"w"))==NULL)
   {
    printf("Can not open the outfile!\n");
    printf("Press any key to exit!\n");
    fclose(in);
    getch();
    exit(0);
   }

   while(!feof(in))
   {
    fputc(encrypt(fgetc(in),n),out);
   }
   printf("\nDecrypt is over!\n");
   fclose(in);
   fclose(out);
   sleep(1);
}


clrscr();

        printf("\nGood Bye!\n");
sleep(3);



    getch();
}
}

那要怎么修改呢