13_18.cpp

C程序参考,简单易懂,是初学者不可少的参考资料

#include<stdio.h>
#include<process.h>
void main()
{  FILE *fp;char  ch;
   if((fp=fopen("d:\\a1.txt","r+"))==NULL)
   {   printf("Cann't Open File d:\\a1.txt");
       exit(0);
   }
ch=fgetc(fp);
   while(!feof(fp))
   {  if(ch>='A'&&ch<='Z') ch=ch+3;
      else if(ch>='a'&&ch<='z') ch=ch-3;
      else if(ch>='0'&&ch<='9') ch=ch+2;
      fseek(fp,-1L,1);
      fputc(ch,fp);
fseek(fp,0L,1);
ch=fgetc(fp);
   }
   fclose(fp);
}