Read from file and store it into array C++ and choose random word

Hello i am very very beginner lvl programmer, how can i make program choose random word? Teacher asked to store words from file into dynamic array? I have tried everything and literally nothing works or is too complicated to understand. Below is simplified program.

#include <iostream>
#include <string>
#include <fstream>

using namespace std;
/* file.txt looks like this:
5
HELLO
BYE
MORNING
HEY
GOOD
*/

void ReadFile() {
  ifstream input("file.txt");
  if (input.fail()) {
    cout << "Something went wrong." << endl;
    input.close();
  } else {
    cout << "Poggers" << endl;
  }
}

void ChooseRandomWord() {
//HOW can i now make program choose a random word from file.txt ChooseRandomWord

}

int main() {
  ReadFile();
  ChooseRandomWord();

  return 0;
}