Is there a way avoid a global array? - c++

Question

A lab assignment that I have for a beginner C++ class involves printing the squareroot of a series of numbers stored in an array. The program itself works, but my teacher does not want us to use global variables.
void assignValue(){
for (int x=0; x<10; x++){
int num;
num = rand() % 100 + 1;
if (num % 2 != 0){
num += 1;
}
arr[x] = num;
}
Here's the main method
int main() {
srand(static_cast<unsigned int>(time(0)));
assignValue();
for (int f = 0; f < 10; f++){
cout << f << setw(8) << right << arr[f];
float square = sqrt(arr[f]);
cout << setw(8) << right << fixed << setprecision(3) << square << endl;
}
The arr is a global variable above the main method.

Answer 1

#include <cstdlib>
#include <ctime>
#include <iostream>
#include <iomanip>
#include <cmath>
void assignValue(int arr[], size_t n) {
for (int i=0; i<n; ++i) {
int num;
num = std::rand() % 100 + 1;
if (num % 2 != 0) {
num += 1;
}
arr[i] = num;
}
}
int main() {
const size_t size = 10;
int arr[size];
std::srand(static_cast<unsigned int>(std::time(0)));
assignValue(arr, size);
for (int i = 0; i < size; ++i){
std::cout << i << std::setw(8) << std::right << arr[i];
float square = std::sqrt(arr[i]);
std::cout << std::setw(8) << std::right << std::fixed << std::setprecision(3) << square << std::endl;
}
return 0;
}

Answer 2

Here is a suggestion for the function taking an array reference:
// headers omitted (you'll need additionally iomanip, ctime, cstdlib, cmath)
// The constant is necessary because the function takes
// a reference to an array *of this specific size*
const size_t ARR_SIZE = 10;
// Take a reference to the array (the array is not copied)
void assignValue(int (&arr)[ARR_SIZE])
{
for (int i = 0; i < ARR_SIZE; i++) {
int num = rand() % 100 + 1;
if (num % 2 != 0) {
num += 1;
}
arr[i] = num;
}
}
You call the function simply with
int main()
{
int arr[ARR_SIZE];
// [...]
assignValue(arr);
// ...
}

Answer 3

The following is a more Core Guideline compliant way of doing this as no pointers, or size information is needed.
#include <cstddef>
#include <cstdlib>
template<typename T, std::size_t N>
void assignValue(T (&arr)[N])
{
for (auto &elem : arr) {
elem = rand() % 100 + 1;
if (elem % 2 != 0) {
elem += 1;
}
}
}
auto
main() -> int
{
constexpr const auto ARRAY_SIZE = 10;
int arr[ARRAY_SIZE];
assignValue(arr);
return 0;
}