Работа с массивами в С++

#include <iostream>
#include <cmath>
#include <clocale>
using namespace std;
int main()
{
    setlocale (LC_ALL, "rus");
    int n, m, x, P = 1, Sp = 0, S = 0;
    double I;
    cin >> m;
    int* mass = new int [255];
    int* mass2 = new int [255];
    for (int i = 0; i < m; i++)
    {
    cout << "mass[" << i << "] = ";
    cin >> n;
    mass[i] = n;
}
for (int i = 0; i < m; i++)
{
    cout << "mass2[" << i << "] = ";
    cin >> x;
    mass2[i] = x;
}
for (int i = 0; i < m; i++)
{
    P = mass[i]*mass2[i];
    Sp = Sp + P;
    S = S + mass[i];
}
I = Sp/S;
cout << I;
delete mass;
delete mass2;
system ("pause");
}

#include <iostream>
#include <cstdlib>
using namespace std;
 
int main() 
{
    int n, x, sumArr =0;
    double sum=0;
    cout << "Input number of elements:" << endl;
    cin >> n;
    int *arr = new int [n];
    for (int i=0; i<n; i++)
    {
        cout << "Input "<< i+1 << "element (1st array): ";
        cin >> arr[i];
        sumArr += arr[i];
    }
    double *arr2 = new double [n];
    for (int i=0; i<n; i++)
    {
        cout << "Input "<< i+1 << " element (2nd array): ";
        cin >> arr2[i];
    }
    system("cls");
    cout << "\nArray 1" << endl;
    for (int i=0; i<n; i++)
    {
        cout << arr[i] << '\t';
    }
    cout << "\nArray 2" << endl;
    for (int i=0; i<n; i++)
    {
        cout << arr2[i] << '\t';
    }
    for (int i=0; i<n; i++)
    {
        sum += arr[i]*arr2[i];
    }
    cout << endl;
    cout << "result: " << sum / sumArr << endl;
    delete [] arr2;
    delete [] arr;
    system("pause");
return 0 ;
}

#include <algorithm>
#include <ctime>
#include <iomanip>
#include <iostream>
#include <iterator>
#include <numeric>
#include <vector>
 
int main() {
 
    srand(time(NULL));
 
    size_t m;
 
    std::cout
        << "Enter the size of the array: ";
    std::cin
        >> m;
 
    std::vector<int> array(m);
    std::vector<float> floatArr(m);
    std::vector<float> result(m);
 
    for (size_t i = 0; i < m; i++) {
 
        array[i] = rand() % 101 - 50;
        floatArr[i] = rand() % 101 - 50;
        floatArr[i] /= rand() % 101 - 50;
 
    }
 
    std::transform(array.begin(), array.end(), floatArr.begin(), result.begin(), std::plus<float>());
 
    std::cout
        << std::endl
        << "Result: "
        << std::accumulate(result.begin(), result.end(), 1.0, std::multiplies<float>()) / std::accumulate(array.begin(), array.end(), 0)
        << std::endl;
 
    std::system("PAUSE");
    return EXIT_SUCCESS;
 
}

#include <algorithm>
#include <ctime>
#include <iomanip>
#include <iterator>
#include <numeric>
#include <vector>