C++ Vectors in a Class - c++

Question

i am working on a worksheet i have for university and the question asks me to "Allow a user to enter 10 numbers from the keyboard into an array" however we have been told that we need to use classes and vectors for this task. When i run my code i get an error stating: "Expression: Vector subscript out of range"
can anyone help?
Array.h
#include <iostream>
#include <vector>
using namespace std;
class Array
{
private:
vector<int> lists;
public:
void fillArray();
void printForwards();
void halfandHalf();
void shiftArrayRight();
Array();
Array(vector<int>);
};
Array.cpp
#include "Array.h"
Array::Array()
{
lists[10];
}
Array::Array(vector<int> lists)
{
this->lists = lists;
}
void Array::fillArray()
{
for (int i = 0; i < 10; i++)
{
cin >> lists[i];
}
}
void Array::printForwards()
{
for (int i = 0; i < 10; i++)
{
cout << lists[i];
}
}
Source.cpp
#include <iostream>
#include "Array.h"
using namespace std;
int main()
{
Array list1,list2;
//fill array 1
list1.fillArray();
//fill array 2
list2.fillArray();
// print array 1
list1.printForwards();
//print array 2
list2.printForwards();
system("pause");
return 0;
}
Thanks in advance

Answer 1

lists[10]; is not going to create a vector of size 10. It is going to try and access the 11th element of an empty vector. If you wanted to create a vector of size 10 then you can use
Array::Array() : lists(std::vector<int>(10, 0)) {}
I would also suggest you change
Array::Array(vector<int> lists)
{
this->lists = lists;
}
To
Array::Array(vector<int> lists) lists(lists) {}
You should also change your for loops to use the vector size() instead of a hard coded value
void Array::fillArray()
{
for (int i = 0; i < lists.size(); i++) // uses size()
{
cin >> lists[i];
}
}
void Array::printForwards()
{
for (int i = 0; i < lists.size(); i++) // uses size()
{
cout << lists[i];
}
}
Or if you have C++11 or higher you can use a ranged based for loop like
void Array::fillArray()
{
for (auto& e : lists)
{
cin >> e;
}
}
void Array::printForwards()
{
for (const auto& e : lists)
{
cout << e;
}
}