Beginner at C++ really struggling w/ Vectors

[jpauly1]

Any help that can be given is greatly appreciated! This is my first C++ assignment and I am really struggling with getting it to print correctly. Long story short, I need to create a lottery app that uses random_shuffle() and sort()on a vector and passes it to a print function that will display the numbers in numerical order. I've gotten the random_shuffle aspect to work but am struggling with the sort() and getting it to print. Right now it is only printing multiple 0's.

void lotto(int highNum, int numSlots, vector<int>& lottoNumbers);
void displayNumbers(vector<int>& lottoNumbers);

int main()
{

   int highNum;
   int numSlots;;
   char repeat = ' ';
   vector<int> lottoNumbers(numSlots);
   
   do
   {
      cout << "Enter the highest number: ";
   
      cin >> highNum;
   
   
      cout << "How many numbers should be generated? ";
   
      cin >> numSlots;
      
      lotto(highNum, numSlots, vector<int> lottoNumbers);
      
      displayNumbers(vector<int> lottoNumbers);
      
      cout << endl;
      
      cout << "Would you like to generate another ticket? (Y or N)";
      
      cin >> repeat;
   }
   while(repeat == 'y' || repeat == 'Y');
}


void lotto(int highNum, int numSlots, vector<int>& lottoNumbers)
{
   vector<int> allNumbers(highNum);
   
   for(int i = 0; i < highNum; i++)
   {
      allNumbers[i] = i + 1;    
   }
   
   random_shuffle(allNumbers.begin(), allNumbers.end());
   
   
   for(int j = 0; j < numSlots; j++)
   {
      lottoNumbers[j] = allNumbers[j];
   }
   
   sort(lottoNumbers.begin(), lottoNumbers.end());
}



void displayNumbers(vector<int>& lottoNumbers)
{
   
   for(int p = 0; p < lottoNumbers.size(); p++)
   {
      cout << lottoNumbers[p] << " ";
   }
}

[JLBorges]

#include <iostream>
#include <vector>
#include <algorithm>
#include <numeric>
#include <random>
#include <ctime>

std::vector<int> generate_lotto_numbers( int high_num, std::size_t num_slots );
void display_numbers( const std::vector<int>& lotto_numbers );

int main()
{
    char repeat = ' ';
    do
    {
        int high_num;
        std::cout << "Enter the highest number (999-999999): ";
        std::cin >> high_num;
        if( high_num < 999 ) high_num = 999 ; // ideally, avoid such magic numbers
        else if( high_num > 999999 ) high_num = 999999 ; // ie. define constants
        // see: https://en.wikipedia.org/wiki/Magic_number_(programming)#Unnamed_numerical_constants 

        int num_slots;
        std::cout << "How many numbers should be generated (1-" << high_num << ")? ";
        std::cin >> num_slots;
        if( num_slots < 1 ) num_slots = 1 ;
        else if( num_slots > high_num ) num_slots = high_num-1 ;

        const std::vector<int> lotto_numbers = generate_lotto_numbers( high_num, num_slots );
        display_numbers(lotto_numbers);

        std::cout << "\nWould you like to generate another ticket? (Y or N): ";
        std::cin >> repeat;
    }
    while( repeat == 'y' || repeat == 'Y' );
}

std::vector<int> generate_lotto_numbers( int high_num, std::size_t num_slots )
{
   std::vector<int> all_numbers(high_num);

   // fill the vector with numbers 1 ... high_num
   // http://en.cppreference.com/w/cpp/algorithm/iota
   std::iota( all_numbers.begin(), all_numbers.end(), 1 ) ;

   // shuffle the numbers (avoid the deprecated std::random_shuffle)
   // http://en.cppreference.com/w/cpp/numeric/random
   static std::mt19937 rng( std::time(nullptr) ) ; // the random number engine
   // http://en.cppreference.com/w/cpp/algorithm/random_shuffle
   std::shuffle( all_numbers.begin(), all_numbers.end(), rng ) ;

   // select the first num_slots numbers of the randomly shuffled sequence
   // this simulates a random selection without replacement
   std::vector<int> lotto_numbers( all_numbers.begin(), all_numbers.begin()+num_slots ) ;

   // sort the selected numbers
   std::sort( lotto_numbers.begin(), lotto_numbers.end() );

   return lotto_numbers ; // and return the selected numbers
}

void display_numbers( const std::vector<int>& lotto_numbers )
{
    std::cout << "the randomly drawn " << lotto_numbers.size() << " numbers are\n" ;

    // http://www.stroustrup.com/C++11FAQ.html#for
    for( int number : lotto_numbers ) std::cout << number << ' ' ;
    std::cout << '\n' ;
}

[jpauly1]

Thanks! This really helped me get an idea on how to pass the vector and display the results. Appreciate the help.