#include <cmath>

void triangle_area(double a,double b,double c,double &area,double &perimeter){
  double s, asq;

  if ( a <= 0 || b <= 0 || c <= 0 ) {
    area = 0.0;
    perimeter = 0.0;
    return;
  }
  perimeter = a + b + c;
  s = perimeter/2.0;
  asq = s* (s-a) *(s-b)*(s-c);
  if ( asq <= 0 ) {
    area = 0.0;
    perimeter = 0.0;
    return;
  }
  area = sqrt(asq);
  return;
}

#ifdef TEST
#include <iostream>
using namespace std;

void triangle_area(double a,double b,double c,double &area,double &p);

int main()
{
  double a,b,c,area,perimeter;

  while (1){
    cout << "Give me the lengths of the three sides of a triangle.";
    cin >> a >> b >> c;
    if ( a == 0 && b == 0 && c == 0 ) break;
    triangle_area(a,b,c,area,perimeter);
    cout << "For sides a = " << a << " b = " << b << " c = " << c << ":\n";
    if ( area == 0.0 && perimeter == 0.0 ) cout << "that is not a triangle!\n";
    else cout << "Area = " << area << " perimeter = " << perimeter << endl;
  }

  return 0;
}
#endif