Cannot use .begin() or .end() on an array

Arrays have no member functions as they aren't a class type. This is what the error is saying.

You can use std::begin(arr) and std::end(arr) from the <iterator> header instead. This also works with types that do have .begin() and .end() members, via overloading:

#include <array>#include <vector>#include <iterator>int main(){    int c_array[5] = {};    std::array<int, 5> cpp_array = {};    std::vector<int> cpp_dynarray(5);    auto c_array_begin = std::begin(c_array); // = c_array + 0    auto c_array_end = std::end(c_array);     // = c_array + 5    auto cpp_array_begin = std::begin(cpp_array); // = cpp_array.begin()    auto cpp_array_end = std::end(cpp_array);     // = cpp_array.end()    auto cpp_dynarray_begin = std::begin(cpp_dynarray); // = cpp_dynarray.begin()    auto cpp_dynarray_end = std::end(cpp_dynarray);     // = cpp_dynarray.end()}

For a standard fixed-length C array, you can just write

int c_array[] = {1,3,5,7,9}, acc = 0;for (auto it : c_array) {    acc += it;}

The compiler does the behind-the-scenes work, eliminating the need to create all those begin and end iterators.

In C++, arrays are not classes and therefore do not have any member methods. They do behave like pointers in some contexts. You can take advantage of this by modifying your code:

#include <iostream>using namespace std;int main(){    int * mypointer;    const int SIZE = 5;    int arr[SIZE] = {1,3,5,7,9};    mypointer = arr;    for(auto it = arr; it != arr + SIZE; ++it) {        cout<<*mypointer<<endl;        mypointer++;    }    return 0;}

Of course, this means that mypointer and it both contain the same address, so you don't need both of them.