#include<stdio.h> 

#include<stdlib.h>

int main(void)

{FILE *fp1,*fp2;

int n,i;

char a[100],b[100],c[100],d[100];

printf("输入明文文件名：");

gets(a);

printf("输入n的值：");

scanf("%d",&n);

fp1=fopen(a,"w");

fprintf(fp1,"This is a C file!"); 

fclose(fp1);

fp1=fopen(a,"r");

fgets(c,18,fp1);

fclose(fp1);

printf("输入密文文件名：");

gets(d);

fp2=fopen(d,"w");

for(i=0;i<19;i++)

{c[i]+=3;

fputc(c[i],fp2);}

fclose(fp2);

printf("加密成功后的密文为：%s",c);

return 0; 

}