Sequence for numbers in a vector - c++

Question

void Numbers()
{
do
{
cout << "Enter the value for the sequence: ";
cin >> K;
if ( K <= 3)
{
cout << "Write a bigger number!" << endl;
}
} while(K <= 3);
cout << "Enter the first number: ";
cin >> N;
}
double Sum()
{
vector<double> arr(K);
arr.push_back(N);
for (int i=0; i < arr.size(); i++)
arr.at(i)=i;
cout << "Vector contains: ";
for (int i=0; i < arr.size(); i++)
cout << arr.at(i);
int main()
{
Numbers();
Sum();
return 0;
}
Write a program that generates sequence of K (K > 3) numbers as follows:
The members of the above sequence are obtained as follows:
the first element is N;
the second one is N + 1;
the third - N * 2.
In other words, we consistently add 1 to each element and put it to the end of the sequence, then multiply it by 2 and again, put the product to the end of the sequence. Choose and implement a suitable data structure that can be used to generate the above sequence of numbers.
The users should enter values for K and first element N.
This is my current code(in the code above). I don`t realy know where to go from here onward to be completely honest. Any suggestions on how to create the sequence from the condition above?

Answer 1

You can use this code to get what you want:
#include <iostream>
#include <vector>
using namespace std;
vector<double> createOutputArray (int K, int N)
{
vector<double> arr;
int tmp = N;
arr.push_back(tmp);
for(int i=1; i+2<=K; i+=2)
{
arr.push_back(++tmp);
arr.push_back(tmp * 2);
tmp *= 2;
}
if(K % 2 == 0)
arr.push_back(++tmp);
return arr;
}
int main()
{
int K;
double N;
do
{
cout << "Enter the value for the sequence: ";
cin >> K;
if ( K <= 3)
{
cout << "Write a bigger number!" << endl;
}
} while(K <= 3);
cout << "Enter the first number: ";
cin >> N;
vector<double> output = createOutputArray(K, N);
for (int i=0; i < output.size(); i++)
{
cout << output.at(i);
if(i < output.size()-1)
cout << ",";
else
cout << endl;
}
return 0;
}

Answer 2

Here is one possibility, using a generator to produce the next element in the sequence.
class Seq
{
public:
Seq(int n) : n(n) {}
int operator*() const { return n; }
Seq operator++(int)
{
Seq old(n);
n = fns[fn](n);
fn = 1 - fn;
return old;
}
private:
int n;
int fn = 0;
std::function<int(int)> fns[2] = {[](int x) { return x + 1; },
[](int x) { return x * 2; }};
};
int main()
{
int N = 1;
int K = 20;
Seq seq(N);
for (int i = 0; i < K; i++)
{
std::cout << *seq++ << ' ';
}
std::cout << std::endl;
}