Novice Coder here: C++ Copying vector into array using functions - c++

Question

Beginner here trying to understand the fundamentals of functions, passing my reference, and vectors/arrays.
My code reads a large data file into a vector. I then, somehow, need to convert the vector into an array, sort the array, and read the output. I believe my issue lies within my attempt to convert the vector to an array.
using namespace std;
//function prototype
int readInput(vector<int> &vect);
void sort(int[], int);
void showArray(int[], int);
int main()
{
vector<int> values;
int sum, avg;
sum = readInput(values);
const int SIZE = values.size(); //ISSUE LIES HERE
int arr[SIZE]; //and here
sort(arr, SIZE);
showArray(arr, SIZE);
avg = sum / values.size();
//cout << "The average is: " << avg;
return 0;
}
int readInput(vector<int> &vect)
{
int count;
int total = 0;
ifstream inputFile("TopicFin.txt"); //open file
if(!inputFile)
{
return 0; // if file is not found, return 0
}
while(inputFile >> count) //read file
vect.push_back(count); //add to file
for (int count = 0; count < vect.size(); count++)
total+=vect[count]; //sum data in vector
return total;
}
void sort(int array[], int size)
{
int startScan, minIndex, minValue;
for(startScan = 0; startScan < (size-1); startScan++)
{
minIndex = startScan;
minValue = array[startScan];
for(int index = startScan + 1; index < size; index++)
{
if (array[index] < minValue)
{
minValue = array[index];
minIndex = index;
}
}
array[minIndex] = array[startScan];
array[startScan] = minValue;
}
}
void showArray(const int array[], int size)
{
for(int count = 0; count < size; count++)
cout << array[count] << " " << endl;
}

Answer 1

You don't need to convert the vector to an array. You can sort the vector directly.
std::sort(values.begin(), values.end())
More info on sort here: http://www.cplusplus.com/reference/algorithm/sort/
I will add that in general, you should never use arrays, especially as a new C++ programmer. They are much more complicated than vectors, and are almost never useful in normal C++ code.
http://www.parashift.com/c++-faq/arrays-are-evil.html

Answer 2

Let me preface by saying that, while this is a good thing to do for learning, converting vectors to arrays is probably not something you should do in real code. In reality, you'd use std::sort to sort your vector.
The root of the issue is that you can't declare an array of size that is unknown at compile-time with the int arr[SIZE] syntax.
const int SIZE = values.size();
The value of this is known when the code is executed, but not at compile time. Therefore int arr[SIZE]; cannot work unlike, say, int arr[100]. To declare an array for which you know the size at runtime, you can do it dynamically like
int* arr = new int[size];
and then you are also forced to delete the array manually.

Answer 3

As seanmcl said, you don't need to convert to an array in order to sort. However, if what you want to do is an exercise in writing a sorting function, then you could simply use values.begin() since the elements of vectors are contiguous. (This is not true for other containers.)