Is it difference between 0 and -0 in c++

Question

I want to create a cycled linked list and I need to find max and min values in it, so I need some checkpoint to stop, and I want to do that with -0 in first element(it will be just a checkpoint not anything else). I don't want to use any else value because user can input new data into the list, if user inputs -0 I will simply replace it on 0 because from math side it is no difference between them (I don't use eternally-small digits :) ). I use integer values.

question is not profitable now. I try it and the result is they are same:

#include <iostream>

using namespace std;

int main() {
    if(0 != -0){
        cout << "they are different!";
    }else{
        cout << "they are same";
    }

    return 0;
}

Thanks to all.

Answer 1

As in maths 0 and -0 are the same value. You can not differentiate them in any way and so you can use this condition as you describe it.

Answer 2

Integer values in the nearly universal twos-complement system can't be negative zero - there's no representation for them. Negative zero simply doesn't exist.

Negative zero is possible with IEEE floating point numbers, but don't come about very often. Multiplying a negative number by 0.0 will do it.

I'd suggest finding another sentinel value.

Answer 3

This would require you store ints as doubles, mind. But you could do something like this.

signbit probably does the trick. If not, try taking the reciprocal. 1/+0.0 = +inf, 1/-0.0 = -inf. As a last ditch effort, do something like:

double d=-0.0;
bool is_neg = (*(uint64_t*)&d)&0x8000000000000000;

Answer 4

Use NaN as a checkpoint:

#include <iostream>
#include <limits>
struct cll {
  double value;
  cll * next;
};
int main() {
  int N = 5;
  double input[] = {1,2,3,4,5};
  cll * first = new cll;
  first->value = std::numeric_limits<double>::quiet_NaN();
  cll * next = first;
  for (int i = 0; i < N; ++i) {
    cll * last = new cll;
    next->next = last;
    last->value = input[i];
    last->next = first;
    next = last;
  }
  next = next->next;
  next = next->next;
  while (next->value == next->value)  {
    next = next->next;
  }
  next = next->next;
  while (next->value == next->value) {
    std::cout << next->value << '\n';
    next = next->next;
  }
  return 0;
}