在 function 之外使用向量值

Question

Background

We're creating a blackjack game, and we want to deal cards to a player. We've made a function that creates a vector of numbers, and we've also been able to "shuffle" those numbers. What we want to do now is take that vector shuffled_cardvals and distribute the values to the dealer and the player.

Our problem is that we can't get shuffled_cardvals to work outside of the function. From perusing other posts, we're fairly certain our issue is that because shuffled_cardvals is used inside the function shuffle(), it doesn't exist outside of that function.

As such, we know the problem, but we can't figure out how to fix it.

Code

Here's our code. We're using a source file and a header file, as we thought that would make things a bit cleaner.

main.cpp

 #include <iostream>
 #include <cmath>
 #include <string>
 #include <vector>
 #include <algorithm>
 #include <sstream>
 #include "blackjack_header_functions.hpp"
 #include "BlackjackClass.hpp"

int main() {

//extern int choice;
// Intro
std::cout << "Good Evening. This is Samuel L. Jackson. Welcome to BlackJack(son). \n";

// output initial face value of cards
std::cout << "Initial face values for each player: ";

int facevalue = 0;
std::cout << "\n";

//shuffle the cards and output the results
shuffle();


// take the player to "the hub"
selectionMenu();

//std::cout << "your choice is " << choice << " biatch\n";

 return 0;
}

blackjack_header_functions.hpp

#include <iostream>
#include <algorithm>
#include <vector>
#include <string>
#include <ctime>
#include <cstdlib>

void selectionMenu();
void DetermineWinner();
void shuffle();

std::vector <std::string> cards = { "AC" , "AH" , "AS" , "AD" ,"KC" , "KH" , "KS" , "KD" , 
"QC" , "QH" , "QS" , "QD", "JC" , "JH" , "JS" , "JD" , "10C" , "10H" , "10S" , "10D" ,
"9C" , "9H" , "9S" , "9D" ,"8C" , "8H" , "8S" , "8D" , "7C" , "7H" , "7S" , "7D" , 
"6C" , "6H" , "6S" , "6D" , "5C" , "5H" , "5S" , "5D" , "4C" , "4H" , "4S" , "4D" , 
"3C" ,"3H" , "3S" , "3D" , "2C" , "2H" , "2S" , "2D" };


std::vector <int> cardvals = {
 2, 2, 2, 2,
 3, 3, 3, 3, 
 4, 4, 4, 4,
 5, 5, 5, 5,  
 6, 6, 6, 6,
 7, 7, 7, 7, 
 8, 8, 8, 8,
 9, 9, 9, 9, 
 10, 10, 10, 10,
 10, 10, 10, 10,
 10, 10, 10, 10,
 10, 10, 10, 10,};



std::vector <int> shuffled_cardvals = {};


std::vector <int> &x;

void shuffle(){

// First, generate a random seed for the card shuffling process.
// If we don't do this step, every time we call random_shuffle(),
// we'll get the same order of cards for our shuffled deck, making
// it not very random.

std::srand(std::time(0));

// Next, shuffle the cards and their face values
std::random_shuffle(cards.begin(), cards.end());
std::random_shuffle(cardvals.begin(), cardvals.end());

// then, put the shuffled cards in a new vector called shuffled_deck
for(int i =  0; i < cards.size(); i++) {shuffled_deck.push_back(cards[i]);}

// do it for the face values too
std::vector <int> shuffled_cardvals = {};
for(int i =  0; i < cardvals.size(); i++) {shuffled_cardvals.push_back(cardvals[i]);}

// finally, output the shuffled deck to the console
std::cout << "Shuffled deck: \n";
for(int i =  0; i < shuffled_deck.size(); i++)  {std::cout << shuffled_deck[i] << " ";}

std::cout << "\n" << "Shuffled card values: \n";
for(int i =  0; i < shuffled_cardvals.size(); i++)  {std::cout << shuffled_cardvals[i] << " ";}

 }

   void Deal(std::vector <int> &x) {

    int dealerhand = 0;
    int playerhand = 0;

    for(int i = 0; i < 4; i++) {

    dealerhand = dealerhand + x[i];
    playerhand = playerhand + x[i+1];

    }

    std::cout << "\n" << dealerhand << "\n" << playerhand;

    }

Console Output (Edited/Fixed 1/4/21)

      In file included from main.cpp:100:
 blackjack_header_functions.hpp:38:20: error: 'x' declared as reference but 
 not initialized
    38 | std::vector <int> &x;
       |                    ^
 blackjack_header_functions.hpp: In function 'void shuffle()':
 blackjack_header_functions.hpp:54:45: error: 'shuffled_deck' was not 
 declared in this scope
    54 |     for(int i =  0; i < cards.size(); i++) 
              {shuffled_deck.push_back(cards[i]);}
       |        ^~~~~~~~~~~~~
 blackjack_header_functions.hpp:62:25: error: 'shuffled_deck' was not 
 declared in this scope
    62 |     for(int i =  0; i < shuffled_deck.size(); i++)  {std::cout << 
         shuffled_deck[i] << " ";} ^~~~~~~~~~~~~
       |                         

Disclaimer

My friend and I are trying to start learning C++ together over winter break, and we're complete noobs. The code right now is in a very unfinished state, and we're sure it already has plenty of issues. Any help is appreciated!

Answer 1

Okay a few things which I am kinda worried about.

1. std::vector <int> cardvals and std::vector <std::string> cards is initialised in the header which you probably dont want. I would recommend declaring it as extern and initialising it in your .cpp . The reason for this is that each translation unit would get their own instance of that array which will cause headache:)

2. It is possible to declare the two arrays globally but usually not recommended. I would create functions which will create such arrays but it is fine the way it is.

3. What are you trying to achieve with std::vector <int> &x; . I am sure std::vector <int> x; will solve your problems:)

Since you are going for C++ instead of C, you should also write the things a bit more object orientated instead of declaring things globally which a few people consider a bad habit.