Відповідь:

C++ code:

#include <iostream>

class Number{

private:

int a,b,c;

int d;

public:

Number();

Number(int,int,int,int);

Number(const Number&);

~Number() = default;

bool check();

void exp();

};

Number::Number(){

a = 0;

b = 0;

c = 0;

d = 0;

}

Number::Number(int a,int b,int c,int d){

this->a = a;

this->b = b;

this->c = c;

this->d = d;

}

Number::Number(const Number& object){

this->a = object.a;

this->b = object.b;

this->c = object.c;

this->d = object.d;

}

bool Number::check(){

return (c - d == b && b - d == a);

}

void Number::exp(){

if(this->check()){

 int counter = 0,i = this->a;

 std::cout << i << " ";

 while(counter <= 15){

  i += this->d;

  std::cout << i << " ";

  counter++;

 }

}

else{

 std::cout << "This is not a progression" << std::endl;

}

}

int main(){

Number obj(4,12,20,8);

obj.exp();

return 0;      

}