setjmploop.cpp

#include <cassert>
#include <climits>
#include <csetjmp>
#include <cstdlib>
#include <cstring>
#include <cctype>

#include <algorithm>
#include <array>
#include <atomic>
#include <chrono>
#include <deque>
#include <fstream>
#include <iomanip>
#include <iostream>
#include <iterator>
#include <list>
#include <map>
#include <memory>
#include <mutex>
#include <random>
#include <regex>
#include <set>
#include <sstream>
#include <string>
#include <utility>
#include <vector>
#include <thread>
#include <type_traits>
#include <typeinfo>
#include <tuple>
#include <unordered_set>


using namespace std;

constexpr int Width = 60;
#define DBG(x) { cout << left << setw(Width) << #x << boolalpha << (x) << endl; }
#define DBG_CONT(x) { cout << left << setw(Width) << #x; for(auto const& _name : (x)) \
	cout << boolalpha << _name << " "; cout << endl; }

#define BARK cout << __PRETTY_FUNCTION__ << endl;

template<typename State>
class Loop
{
	enum ReturnValue{
		FirstIteration = 0,
		ContinueLoop = 1,
		BreakLoop = 2
	};

public:
	Loop(State& s) : state_(s) {}

	template<typename Body, typename Condition>
	void execute(Body b, Condition c){
		switch(setjmp(loopBuffer_)){
		case FirstIteration:
		case ContinueLoop:
			if(!c(state_)){
				longjmp(loopBuffer_, BreakLoop);
			}else{
				b(state_);
				longjmp(loopBuffer_, ContinueLoop);
			}
		}
	}

private:
	State& state_;
	std::jmp_buf loopBuffer_;
};

struct AveragingLoopState
{
	int lastRead;
	int count;
	int sum;
};

void loopBody(AveragingLoopState& s){
	if(!(cin >> s.lastRead)){ s.lastRead = 0; }
	if(s.lastRead){
		++s.count;
		s.sum += s.lastRead;
	}
}

bool loopCondition(AveragingLoopState const& s){
	return s.lastRead;
}

int main()
{
	AveragingLoopState s;
	s.lastRead = -1;
	s.count = 0;
	s.sum = 0;
	Loop<AveragingLoopState> loop(s);
	loop.execute(&loopBody, &loopCondition);
	cout << "Srednia to: " << static_cast<double>(s.sum) / s.count << endl;
}