Thread: How to reset a pointer in a loop?

I'm making this program to check a number, and see if it's valid.

It is reading the numbers in from a text file, and the loop is made to make it keep taking in the numbers from the text file, until it reaches eof.

Problem is, the second time it runs through the loop there occur some errors in the part with the pointer 'i'. After the first round, the integers values gets all wrong. When I try to set i = 0, it crashes my compiler.

Please take a look and let me hear if you know what to do.

Code:

int Iday, Imonth, Iyear, Ictrlnr, Igen, test = 0;

char input[12], day[3], month[3], year[3], ctrlnr[4], gen[2];

char* i = input;

  ifstream b_file ( "testen.txt" );

  while(!b_file.eof())
  {

  b_file >> input;

  cout << endl << input;

  //cout << "Indtast cprnr. i formatet xxxxxx-xxxx ";
  //cin  >> input;

  if(input[11]!='\0')
    test = 1;

  strncpy(day, i, 2);
  i += 2;

  strncpy(month, i, 2);
  i += 2;

  strncpy(year, i, 2);
  i += 3;

  strncpy(ctrlnr, i, 3);
  i += 3;

  strncpy(gen, i, 1);

  Iday = atoi(day);
  Imonth = atoi(month);
  Iyear = atoi(year);
  Ictrlnr = atoi(ctrlnr);
  Igen = atoi(gen);

  cout << endl << Iday << Imonth << Iyear << "-" << Ictrlnr << Igen;

  if(Imonth == 1 || Imonth == 3 || Imonth == 5 || Imonth == 7 || Imonth == 9 || Imonth == 11)
  {
    if(Iday > 31)
      test = 1;
  }
  else if(Imonth == 4 || Imonth == 6 || Imonth == 8 || Imonth == 10 || Imonth == 12)
  {
    if(Iday > 30)
      test = 1;
  }
  else if(Imonth == 2)
  {
    if(Iyear%4 == 0)
    {
      if(Iday > 29)
        test = 1;
    }
    else if(!Iyear%4 == 0)
    {
      if(Iday > 28)
        test = 1;
    }
  }
  else if(Imonth > 12)
    test = 1;

  if(Iyear > 99)
    test = 1;

  if(Iday > 31)
    test = 1;


  if(test == 0)
    cout << endl << input <<" is a valid cprnr. ";
  else if(test == 1)
    cout << endl << input << " is not a valid cprnr. ";
  }
  cin  >> test;

  return 0;
}

Setting a pointer to zero is bad. Remember that a pointer is nothing more than a memory address with special tools to help you access what is stored at the address. Guess what is stored at memory address 0.

Keep that in mind and you should be able to figure out a better solution on your own.

You don't assign 0 to i, as i isn't an index it's an address. Instead assign input to i after each read in from file