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#include <iostream>
#include <queue>
#include <cmath>
 
class C {
protected:
  double a, b;
public:
  C() {}
  C(double a, double b) { this->a = a; this->b = b; }
  friend double abs(C c) { return sqrt(c.a * c.a + c.b * c.b); }
  friend std::ostream &operator<<(std::ostream &s, C &c) {
    s << '(' << c.a << ',' << c.b << ')';
    return s;
  }
};
 
double myabs(C c) { return sqrt(c.a * c.a + c.b * c.b); }
 
class CCompare : C {
public:
  bool operator()(C &r, C &s) { return myabs(r) < myabs(s); }
};
 
int main() {
  C c;
  std::priority_queue<C, std::vector<C>, CCompare> pq;
  pq.push(C(3, 1));
  pq.push(C(4, 1));
  pq.push(C(5, 9));
  pq.push(C(2, 6));
  pq.push(C(5, 3));
  while (!pq.empty()) {
    c = pq.top();
    pq.pop();
    std::cout << c << std::endl;
  }
  return 0;
}
 
 

prog.cpp: In function 'double myabs(C)':
prog.cpp:7: error: 'double C::a' is protected
prog.cpp:18: error: within this context
prog.cpp:7: error: 'double C::a' is protected
prog.cpp:18: error: within this context
prog.cpp:7: error: 'double C::b' is protected
prog.cpp:18: error: within this context
prog.cpp:7: error: 'double C::b' is protected
prog.cpp:18: error: within this context

Standard output is empty