How to combine random filling of an array and searching for a prime number in it?

Question

C++ / C#

There is a program in which there is a function for searching for prime numbers. If everything is extremely simple with one number, then how to look for prime numbers in an array? Here is the code. I know that the function is wrong, but what needs to be changed so that there is a search for a prime number in the array?

#include "stdafx.h"
#include <iostream> 
#include <cstdlib>
#include <ctime>
using namespace std;

int is_prime(int a[5])
{
  
  if (a[5] == 1) return 1;
  int number = 0;
  for (int i = 2; i <= a[5]; i++)
    if (a[5] %i == 0) number++;
  if (number == 1) return 1;
  else return 0;
}

int main()
{
  srand(time(NULL));
  int a[5];
  for (int k = 0; k < 5; k++) {
    a[k] = rand() % 21;
    cout << a[k] << "\n";
  }
  int c = is_prime(a);
    if (c == 1) cout << "is prime";
  else cout << "is not prime";
    return 0;
  system("pause");
}

Answer 1

1. You should have 2 nested loops in is_prime: 1 loop over the array elements, the second (nested) from 2 to a[i] - checking for a prime number. Now - only one and that one is not correct (due to indexing).
2.And deal with array indexing, it looks like you don't understand what you are doing.