Exercise on pure virtual function

[zio_mangrovia]

I'm not able to understand solution about the following exercise where, given this code, It asks to write C++ code which read from standard input positive value N and, for N times, It has to read temperature values from 2 sensors and It has to writes their arithmetic average to standard output.

class Sensor {
public:
   virtual int get_value(void) =0;
};

class Filter {
public:
virtual int filter(int value) =0;
};

class TempSensor : public Sensor {
   Filter* tf;
   int value;
   public:
      TempSensor(Filter* f): tf(f);
      int read(void);
      int get_value(void);
};

class KFilter : public Filter {
// data structures for filtering
public:
   int filter(int value);
};

int TempSensor::read(void)
{
   // read value from hardware
}

int TempSensor::get_temp(void)
{
   value = read();
   return tf->filter(value);
}

int KFilter::filter(int value)
{
   // implementation of filter algorithm
}

Solution:

int
main()
{
   int N;
   cin >> N;
   KFilter kf1;
   KFilter kf2;
   TempSensor ts1(&kf1);
   TempSensor ts2(&kf2);
   for (int i = 0; i < N; i++) {
      ts1.read();
      int v1 = ts1.get_temp();
      ts2.read();
      int v2 = ts2.get_temp();
      cout << (v1 + v2)/2 < endl;
   }
}

1. I think there is error because 'get_temp()' function member is not declared inside TempSensor class, I see only your definition. Pheraps get_temp() and get_value() are the same thing ?
2. In solution, the first step is to read sensor value by ts1.read() but next statement 'ts1.get_temp()' (I suppose that 'get_temp' was the same function 'get_value') read again sensor value and filters it. What necessary to read sensor value twice ?

I think this solution code is wrong, what do you think ?

[2kaud]

1) probably.
2) no.

This is not good code. I suspect it's very old code from wherever it was obtained as it uses void for function parameter which was c style and not used in C++. My advice is to scrap it and write your own. For the given problem it is vastly over-engineered (unless the exercise is to use derived classes).

[2kaud]

Based upon the given design, consider as a starting point:

#include <iostream>
#include <random>

std::mt19937 gen(std::random_device {}());
std::uniform_int_distribution<int> rnd(12, 25);

class Sensor {
public:
	virtual int get_value() = 0;
};

class Filter {
public:
	virtual int filter(int value) const = 0;
};

class TempSensor : public Sensor {
	const Filter* tf {};
	int value {};
public:
	TempSensor(const Filter* f) : tf(f) {};
	void read();
	int get_value() override;
};

class KFilter : public Filter {
	// data structures for filtering
public:
	int filter(int value) const override;
};

void TempSensor::read() {
	// read value from hardware
	value = rnd(gen);	// For testing
}

int TempSensor::get_value() {
	read();
	return tf->filter(value);
}

int KFilter::filter(int value) const {
	// implementation of filter algorithm
	return value - 10;
}

int main() {
	int N {};

	std::cout << "Enter number of values: ";
	std::cin >> N;

	KFilter kf1;
	KFilter kf2;
	TempSensor ts1(&kf1);
	TempSensor ts2(&kf2);

	for (int i {}; i < N; ++i)
		std::cout << (ts1.get_value() + ts2.get_value()) / 2 << '\n';
}

[zio_mangrovia]

1) probably.
2) no.

This is not good code. I suspect it's very old code from wherever it was obtained as it uses void for function parameter which was c style and not used in C++. My advice is to scrap it and write your own. For the given problem it is vastly over-engineered (unless the exercise is to use derived classes).

The exercise requires to use derived classes
I understand that this one is not good code but It's a university exam and now I have to understand just this code, not implement goot code.

you're okay with me that It doesn't necessary to use both ts1.read() and ts1.get_temp() (that is ts1.get_value) ? ts1.get_value read again sensor value. So I have 2 reads for the same sensor, I think It's wrong.

ts1.read();
      int v1 = ts1.get_temp();
      ts2.read();
      int v2 = ts2.get_temp();

thanks again

[2kaud]

To help to learn C++ consider:
https://www.learncpp.com/

[zio_mangrovia]

To help to learn C++ consider:
https://www.learncpp.com/

what mistake did I make in my question please ?