Here is an example of a full code that demonstrates the use of a template function
to calculate the average value of an array:

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#include <iostream>

template <typename T, size_t N>
double average(T(&arr)[N]) {
    T sum = 0;
    for (size_t i = 0; i < N; i++) {
        sum += arr[i];
    }
    return (double)sum / N;
}

int main() {
    int arr1[] = { 1, 2, 3, 4, 5 };
    double arr2[] = { 1.1, 2.2, 3.3, 4.4, 5.5 };

    std::cout << "average of arr1: " << average(arr1) << std::endl;
    std::cout << "average of arr2: " << average(arr2) << std::endl;

    return 0;
}
In this code, the average() template function takes an array arr of type T and
size N as an argument, it calculates the sum of all elements and returns the
average value.

In the main() function, we define two arrays, arr1 and arr2, of type int and
double, respectively, and call the average() function with these arrays.

It's important to note that, the size of the array is passed as a non-type
template parameter, it means that the size of the array must be known at
compile-time, this means you can't use this function with dynamically allocated 
arrays.

he efficiency of using a template function to calculate the average value of an 
array compared to using a normal array or a pointer array depends on the specific
use case and the rest of the code.

When using a template function, the type and size of the array are passed as 
template parameters, which allows the compiler to generate optimized machine code 
for the specific array type and size at compile-time. This can make the template
function more efficient than a normal function that uses a void pointer or a
function that is specialized for a specific type.

Using a normal array is more efficient than using a pointer array in most cases,
because the memory for the array is allocated in a contiguous block, which allows 
better cache utilization and faster access to elements. When you use a pointer 
array, you need to dereference the pointer to access the array elements, which 
can be less efficient than accessing the elements of a normal array.

In terms of use cases, if you need to perform the same operation on arrays of 
different types and sizes, using a template function is a good choice, as it 
allows you to write a single function that can handle any type of array. On
the other hand, if you only need to work with arrays of a specific type and size, 
using a normal array or a specialized function may be more efficient and easier
to read.

In summary, both template function and normal arrays have their own strengths 
and weaknesses and the choice of which one to use depends on the specific 
requirements of the project. Using a template function can be more flexible,
but it can be less efficient than using a specialized function or a normal array.
Using a normal array can be more efficient than using a pointer array, but it 
can be less flexible in some cases.