C++ Bc. 12 cpp

#include <iostream>
#include <sstream>
#include <algorithm>
#include <vector>

struct Chyba
{
   template <typename T> Chyba(T t) : text(t) {}

   std::string text;
};

struct Bod {
  double x, y;
};

typedef std::vector<Bod> Polygon;

double plocha(const Polygon& p)
{
  const int N = p.size();
  
  bool uzavreny = p[0].x == p[N-1].x  || p[0].y == p[N-1].y;

  if ((uzavreny && N < 3) || (!uzavreny && N < 2))
    throw Chyba("polygon musi mit minimalne 3 vrcholy");

  double s = 0;
  if (!uzavreny)
    s += (p[N-1].x - p[0].x)*(p[N-1].y + p[0].y);

  for (int i=0; i<N-1; i++)
    s += (p[i+1].x - p[i].x)*(p[i+1].y + p[i].y);

  return std::abs(s/2);
}

int main()
{
  using namespace std;
  
  Polygon p;

  istringstream input("1 1  0 2  -1 1  -1 -1  1 -1");
  Bod b;
  while (input >> b.x >> b.y) p.push_back(b);

  try
    {
      cout << "Plocha = " << plocha(p);
    }
  catch(Chyba &ch)
    {
      cout << ch.text << endl;
    }
}

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