Шаблон сумма элементов двух массивов

template<class T, class U>
    auto sum(const T& x, const U& y) -> decltype(x - y)
    {
        return x + y;
    }

 
#include <iostream>
using namespace std;
int main()
{
    const int size = 10;
    int arr1[size];
    int arr2[size];
    int arrs[size];
    cout << "Enter the random numbers to fill first array:\n";
    for (int i = 0; i < size; i++)
    {
        cout << "arr1[" << i << "] = ";
        cin >> arr1[i];
    }
    cout << "\nEnter the random numbers to fill second array:\n";
    for (int i = 0; i < size; i++)
    {
        cout << "arr2[" << i << "] = ";
        cin >> arr2[i];
    }
    cout << "\nThe third array with the sum of two arrays:\n";
    for (int i = 0; i < size; i++)
    {
        arrs[i] = arr1[i] + arr2[i];
        sum += arrs[i];
        cout << "arr3[" << i << "] = ";
        cout << arrs[i] << "\n";
    }
    cout << "\n\nPotapenko A.V.\n";
}

#include <iostream> 
#include <iomanip>
 
using namespace std;  
 
template<typename T, typename U> auto TwoArraySum(const T *arr1, int m, const U *arr2, int n) 
{
    T sum1 = 0;
    for(int i = 0; i < m; i++)
            sum1 += arr1[i];
    U sum2 = 0;
    for(int i = 0; i < n; i++)
            sum2 += arr2[i];   
        
    cout << sum1<<endl;
    cout << sum2<<endl;
    auto sum=sum1+sum2;
    return sum;
}
 
  
  
int main()  
{ 
    int a[] = {5 , 10 , 15} ;
    int m = sizeof(a)/sizeof(a[0]);
     
    double b[] = {5.1 , 10 , 15.2} ;
    double n = sizeof(b)/sizeof(b[0]); 
    
    decltype(auto) res=TwoArraySum(a,m,b,n);
    cout << res<<endl;
 
    return 0; 
}

#include <iostream>
#include <type_traits>
 
template<class T, class U, size_t N1, size_t N2>
auto sum(const T (&first)[N1], const U (&second)[N2])
{
    typename std::common_type<T, U>::type sum{};
    for (size_t i = 0; i < N1; ++i)
        sum += first[i];
    for (size_t i = 0; i < N2; ++i)
        sum += second[i];
    return sum;
}
 
int main()
{
    int arr1[] = { 3, 4 };
    double arr2[] = { 1., 2. };
    std::cout << sum(arr1, arr2) << std::endl;
}

template<class T, class U>
    auto sum(const std::valarray<T>& x, const std::valarray<U>& y)
    {
        return x + y;
    }