#include <stdio.h>
#include <string.h>
main()
{
    FILE *fp;
    char s[80],ch,key;
    key=31;
    if((fp=fopen("c:\\0.txt","r+"))==NULL)
    {
        printf("Cannot open file 0.txt");
        getch();
        exit(0);
    }
    fgets(s,80,fp);
    printf("\n%s\n",s);
        rewind(fp);
    while(!feof(fp))
    {
        ch=ch^key;
        fseek(fp,-1L,1);
        fputc(ch,fp);
        fseek(fp,0L,1);
        ch=fgetc(fp);
    }
    fclose(fp);
    fp=fopen("0.txt","r");
    fgets(s,80,fp);
    puts(s);
    fclose(fp);
}