Вступ до STL

#include <iostream>
#include <vector>

using namespace std;
int Sum(const vector<int>& a)
{
    int sum = 0;
    for (int i = 0; i < a.size(); i++)
    {
        int x = a[i];
        if (x < 0)
        {
            x = -x;
        }
        while (x > 0)
        {
            sum += x % 10;
            x /= 10;
        }
    }
    return sum;
}

double AVGplus(const vector<int>& a)
{
    int sum = 0;
    int temp = 0;
    for (int i = 0; i < a.size(); i++)
    {
        if (a[i] > 0)
        {
            sum += a[i];
            temp++;
        }
    }
    return sum / temp;
}

void ShowMin(const vector<int>& a)
{
    int temp = a[0];
    int ind = 0;
    for (int i = 0; i < a.size(); i++)
    {
        if (a[i] < temp)
        {
            temp = a[i];
            ind = i;
        }
    }
    cout << "Min: " << temp << " Index: " << ind << endl;
}

int Best(const vector<int>& a)
{
    int best = a[0], bestTemp = 0;

    for (int i = 0; i < a.size(); i++)
    {
        int temp = 0;
        for (int j = 0; j < a.size(); j++)
        {
            if (a[j] == a[i]) temp++;
        }
        if (temp > bestTemp)
        {
            bestTemp = temp;
            best = a[i];
        }
    }
    return best;
}

int Odd(const vector<int>& a)
{
    int temp = a[0];

    for (int i = 0; i < a.size(); i++)
    {
        if (i % 2 == 0)
        {
            if (a[i] % 3 == 0)
            {
                if (temp < a[i])
                {
                    temp = a[i];
                }
            }

        }
    }
    return temp;
}

void Change(vector<int>& a)
{
    for (int i = 0; i < a.size(); i++)
    {
        cout << a[i] << " ";
    }
    cout << endl;
    int maxE = -1000000, minO = 1000000;
    int posE = -1, posO = -1;
    for (int i = 0; i < a.size(); i++)
    {
        if (a[i] % 2 == 0 && a[i] > maxE)
        {
            maxE = a[i];
            posE = i;
        }
        if (a[i] % 2 != 0 && a[i] < minO)
        {
            minO = a[i];
            posO = i;
        }
    }
    if (posE != -1 && posO != -1)
    {
        swap(a[posE], a[posO]);
    }
    else for (int i = 0; i < a.size(); i++)
    {
        a[i] = 0;
    }

    for (int i = 0; i < a.size(); i++)
    {
        cout << a[i] << " ";
    }
}

void UnionInter(const vector<int>& a, const vector<int>& b) 
{
	int n = a.size();
	int m = b.size();  

    int both[100], onlyOne[100];
    int bC = 0, oC = 0;

    for (int i = 0; i < n; i++) 
    {
        bool found = false;
        for (int j = 0; j < m; j++) 
        {
            if (a[i] == b[j]) 
            {
                found = true;
                break;
            }
        }
        if (found)
            both[bC++] = a[i];
        else
            onlyOne[oC++] = a[i];
    }

    for (int j = 0; j < m; j++) 
    {
        bool found = false;
        for (int i = 0; i < n; i++) 
        {
            if (b[j] == a[i]) 
            {
                found = true;
                break;
            }
        }
        if (!found)
        {
            onlyOne[oC++] = b[j];
        }
    }
    cout << "\na) Both array: ";
    for (int i = 0; i < bC; i++)
    {
        cout << both[i] << " ";
    }
    cout << "\nb) Only in 1 array: ";
    for (int i = 0; i < oC; i++)
    {
        cout << onlyOne[i] << " ";
    }
    cout << endl;
}

int main()
{
    vector<int>a{ 10,23,-23,-4,90,10 };
    vector<int>b{ 1,23,-3,50,-4,10 };

    cout << "Sum: " << Sum(a) << endl;
    cout << "AVGplus: " << AVGplus(a) << endl;
    ShowMin(a);
    cout << "Best: " << Best(a) << endl;
    cout << "Max/3: " << Odd(a);
    cout << endl<<"Change min_max: "<<endl;
    Change(a);
    UnionInter(a, b);
}