I'm currently taking the introduction to C++ class. I'm currently ahead of my class so the teacher refuses to answer my questions -_-. I've been reading through my book and looking through the web but I can't understand what my mistake is, can anyone give me hints as to what my mistake is?

Also, I know the code is sort of a mess, I've been messing around with it alot to try and figure out the mistake so there are a few variables and instructions that aren't useful, it's just that I couldn't get my function that calculates the average to work so I just programmed the instructions into the main.

I marked the line with the error with ==><== error here.

Code:
#include <iostream>

using namespace std;

int carre(int x);
double average(int a[]);

int main()
{
        int n,
            i,
            m,
            entier[5];
        double moyenne,
               moyenne_carre,
               sum = 0,
               sum_carre = 0;
               
        char check;

        do {
        cout << "\nVeuillez entrer 5 valeures entieres : " <<endl;

        for ( m = 0 ; m <= 4 ; m++ )
            cin >> entier[m];
        

        /*for ( m = 0 ; m <= 4 ; m++)
            sum += entier[m];

        moyenne = sum / 5;*/

        cout << "La moyenne des chiffres est :";
        for ( n = 0 ; n <= 4 ; n++ )
===>         cout << average(entier[n]) << " ";      <===  error here

        /*cout << "Les valeures au carre sont: ";

        for ( i = 0 ; i <= 4 ; i++ )
            cout << carre(entier[i]) << " ";
        
        
        for ( m = 0 ; m <= 4 ; m++ )
            sum_carre += carre(entier[m]);

        moyenne_carre = sum_carre / 5;

        cout << "La moyenne des chiffres au carre est:" << moyenne_carre << endl;
        */
        cout << "\nEncore? (y/n) :";
        cin >> check;

        } while (check == 'y');

cin.sync();
cin.get();
}

int carre(int x)
{
    return x * x;
}

double average(int a[])
{
    int avg = 0, sum = 0, n, i = 0;

    for (n = 0 ; n <= 4 ; n++)
    {    
        sum += a[n];
        i=i++;
    }

    avg = sum/i;

    return avg;
}