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

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;

}

You can treat a vector as an array, there's really no need to convert anything. — user2033018
– user2033018, Commented Nov 7, 2013 at 18:55

seanmcl · Accepted Answer · 2013-11-07 19:20:13Z

5

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

edited Nov 7, 2013 at 19:20

answered Nov 7, 2013 at 18:51

seanmcl

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Comments

DUman · Accepted Answer · 2013-11-07 18:54:54Z

3

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.

answered Nov 7, 2013 at 18:54

DUman

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Klitos Kyriacou · Accepted Answer · 2013-11-07 18:56:10Z

0

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.)

answered Nov 7, 2013 at 18:56

Klitos Kyriacou

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1 Comment

user2033018 Over a year ago

It is for std::array ;)

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