How to increase day by one in C

  int year, month, day;
  sscanf(namelist[2]->d_name, "%2d%2d%2d", &year, &month, &day);
struct tm tmp;
tmp.tm_mday = day;
tmp.tm_mon = month;
tmp.tm_year = year + 2000 - 1900;
time_t epoch = mktime(&tmp);
epoch += 24*60*60;
struct tm *tmp2 = localtime(&epoch);
tmp=*tmp2;
strftime(buffer, SIZE, "%y%m%d", &tmp);

  if (strcmp(buffer, namelist[3]->d_name) != 0) {