C++ foldl

#include <iostream>
#include <assert.h>
using namespace std;

template<typename T>
T foldl(T *array, size_t length, T (*f)(T, T))
{
    assert(length != 0);
    T result = array[0];
    for(size_t i = 1; i < length; ++i)
    {
        result = f(result, array[i]);
    }
    
    return result;
}

template<typename T>
T sub(T a, T b)
{
    return a - b;
}

template<typename T>
T add(T a, T b)
{
    return a + b;
}

int main()
{
    int arr[] = {5, 3, 1};
    cout << foldl(arr, 3, &sub) << endl;
    float arrf[] = {5.1, 3.2, 1.4};
    cout << foldl(arrf, 3, &sub) << endl;
    cout << foldl(arr, 3, &add) << endl;
    cout << foldl(arrf, 3, &add) << endl;
    return 0;
}