Passing Arrays into Functions in C++? [Lottery Numbers]

Question

I am creating a lottery game in C++. I created a function called GetLottoPicks which asks the user for 7 numbers. I have another function called GenWinNums that generates 7 random numbers.

The problem is for the GenWinNums it keeps generating this 7 times: -858993460

I believe I made inputs into the argument int WinningNums[] bu apparently not?

Thank you.

int main()
{
string name;
int choice;
int user_picked[7];
int chosen_lotto[7];

cout << "LITTLETON CITY LOTTO MODEL:" << endl;
cout << "---------------------------" << endl;
cout << " 1) Play Lotto " << endl;
cout << " Q) Quit Program " << endl;
cout << " Please make a selection: ";
cin >> choice;

if (choice == 1)
{
    cout << "\n Please enter your name: ";
    cin >> name;

    getLottoPicks(user_picked);
    GenWinNums(chosen_lotto);

    for(int i = 0; i < 7; i++)
    {
        cout << chosen_lotto[i];    
    }

    for(int i = 0; i < 7; i++)
    {
        cout << user_picked[i];
    }
}

else if (choice == 'Q' || 'q')
{
    exit(0);
}

else 
{
    cout << "That is not a valid choice." << endl;
}

 system("PAUSE");
 return 0;
 }

 int getLottoPicks(int UserTicket[])
 {   
const int amount = 7;
UserTicket[amount];
int ticket = UserTicket[amount];

for (int i = 0; i < amount; i++)
{
    cout << "\n Please enter number " << i + 1 << ":";
    cin >> UserTicket[i];

    while (UserTicket[i] < 1 || UserTicket[i] > 40)

    {
        cout << "Your selection cannot be less than 1 and/or greater than 40. Try Again." << endl;
        cin >> UserTicket[i];
    }

if(i > 0)
    {
        for(int check = 0; check < i; check++)
        {
            while(UserTicket[i] == UserTicket[check])
            {
                cout << "You cannot use the same lotto number twice. Try again: " << endl;
                cin >> UserTicket[i];
            }
        }
}

}

return ticket;
 }

 int GenWinNums(int WinningNums[])
 {
const int amount = 7;
int numbers[amount];
int ticket = WinningNums[amount];

for(int i = 0; i < amount; i++)
{
    numbers[i] = (rand() % 40) + 1;

    while(numbers[i] < 1 || numbers[i] > 40)
    {
        numbers[i] = (rand() % 10) + 1;
    }
    if(i > 0)
    {
        for(int check = 0; check < i; check++)
        {
            while(numbers[i] == numbers[check])
            {
                numbers[i] = (rand() % 10) + 1;
            }
        }
    }
}
return ticket;
 }

possible duplicate of [How do I use arrays in C++?](http://stackoverflow.com/questions/4810664/how-do-i-use-arrays-in-c) — sehe, Nov 16 '12 at 23:28
Believe it or not, you don't know how to use arrays! You called the WinningNums[amount], where amount = 7 and the size of the array is 7! Out of bound! — Afshin Moazami, Nov 16 '12 at 23:42
Well, maybe it's not about the issue. It _is_ about what you need to know, though. — sehe, Nov 16 '12 at 23:44

score 3 · Answer 1 · answered Nov 17 '12 at 00:37

Just for fun, here's a fairly big number of fixes. I'm not going to enumerate them all. basically:

pass fixed size arrays by reference, to avoid unsafe usage
check input errors rigorously, and do it in a single loop
several misguided array assignments that either did nothing or prevented the result being seen by the caller...
use char for the input type (so Q would ever get matched) and prefer aa switch over repeated ifs
See below for a more typical C++ style solution, including a check for WIN or LOSE

Exercise for the reader: seed your rand() generator, or it was pretty simple to win this lottery (pasting in the previous winning ticket :))

Output on a demo run (shows error handling as well):

LITTLETON CITY LOTTO MODEL:
---------------------------
 1) Play Lotto 
 Q) Quit Program 
Please make a selection: 1

 Please enter your name: me

 Please enter number 1:34

 Please enter number 2:7

 Please enter number 3:16

 Please enter number 4:18

 Please enter number 5:24

 Please enter number 6:24
Duplicate entry 24
 Please enter number 6:7
Duplicate entry 7
 Please enter number 6:37

 Please enter number 7:whoops
Bad input 'whoops' discarded
 Please enter number 7:what was the last number again?
Bad input 'what' discarded
 Please enter number 7:Bad input 'was' discarded
 Please enter number 7:Bad input 'the' discarded
 Please enter number 7:Bad input 'last' discarded
 Please enter number 7:Bad input 'number' discarded
 Please enter number 7:Bad input 'again?' discarded
 Please enter number 7:27
User ticket:    7; 16; 18; 24; 27; 34; 37; 
Winning ticket: 7; 16; 18; 24; 27; 34; 36; 
Result of draw: WINNER

.

#include <string>
#include <iostream>

const size_t amount = 7;

void getLottoPicks(int (&ticket)[amount])
{
    for(int i = 0; i < amount; i++)
    {
        do
        {
            std::cout << "\n Please enter number " << i + 1 << ":";
            if(std::cin >> ticket[i])
            {
                if(ticket[i] >= 1 && ticket[i] <= 40)
                {
                    bool ok = true;
                    for(int check = 0; ok && check < i; check++)
                    {
                        ok &= (ticket[i] != ticket[check]);
                    }
                    if(ok)
                    {
                        break;
                    }
                    else
                    {
                        std::cout << "You cannot use the same lotto number twice. Try again." << std::endl;
                    }
                }
                else
                {
                    std::cout << "Your selection cannot be less than 1 and/or greater than 40. Try Again." << std::endl;
                }
            }
            else
            {
                std::cin.clear();
                std::string discard;
                std::cin >> discard;
                std::cout << "Bad input '" << discard << "' discarded";
            }
        }
        while(true);
    }
}

void GenWinNums(int (&winningNumbers)[amount])
{
    for(int i = 0; i < amount; i++)
    {
        winningNumbers[i] = (rand() % 40) + 1;
        while(winningNumbers[i] < 1 || winningNumbers[i] > 40)
        {
            winningNumbers[i] = (rand() % 10) + 1;
        }
        if(i > 0)
        {
            for(int check = 0; check < i; check++)
            {
                while(winningNumbers[i] == winningNumbers[check])
                {
                    winningNumbers[i] = (rand() % 10) + 1;
                }
            }
        }
    }
}
int main()
{
    std::string name;
    char choice;
    std::cout << "LITTLETON CITY LOTTO MODEL:" << std::endl;
    std::cout << "---------------------------" << std::endl;
    std::cout << " 1) Play Lotto " << std::endl;
    std::cout << " Q) Quit Program " << std::endl;
    std::cout << " Please make a selection: ";
    std::cin >> choice;
    switch(choice)
    {
        case '1':
            {
                std::cout << "\n Please enter your name: ";
                std::cin >> name;

                int user_picked[amount];
                int chosen_lotto[amount];

                getLottoPicks(user_picked);
                GenWinNums(chosen_lotto);

                std::cout << "\n";
                for(int i = 0; i < amount; i++)
                {
                    std::cout << user_picked[i] << "; ";
                }
                std::cout << "\n";
                for(int i = 0; i < amount; i++)
                {
                    std::cout << chosen_lotto[i] << "; ";
                }
            }
        case 'Q':
        case 'q':
            return 0;
        default:
            std::cout << "\n That is not a valid choice." << std::endl;
    }
    std::cout << "\n Press enter...";
    std::cin >> choice;
}

More typical C++ solution

#include <string>
#include <iostream>
#include <algorithm>
#include <iterator>
#include <set>

const size_t amount = 7;

typedef std::set<int> ticket_t;

ticket_t getLottoPicks()
{
    ticket_t ticket;
    while (ticket.size() < amount)
    {
        std::cout << "\n Please enter number " << (ticket.size()+1) << ":";

        int entry;
        if(std::cin >> entry)
        {
            if(entry >= 1 && entry <= 40)
            {
                if (ticket.end() != ticket.find(entry))
                    std::cout << "Duplicate entry "  << entry;
                else
                    ticket.insert(entry);
            } else
                std::cout << "Entry out of range [1..40]: "  << entry;

            continue;
        }

        std::cin.clear();
        std::string discard;
        std::cin >> discard;
        std::cout << "Bad input '" << discard << "' discarded";
    }
    return ticket;
}

ticket_t genWinNums()
{
    ticket_t ticket;
    while (ticket.size() < amount)
        ticket.insert(rand() % 40 + 1);
    return ticket;
}

std::ostream& operator<<(std::ostream& os, ticket_t const& t)
{
    std::copy(t.begin(), t.end(), std::ostream_iterator<int>(os, "; "));
    return os;
}

int main()
{
    std::cout << "LITTLETON CITY LOTTO MODEL:" << std::endl;
    std::cout << "---------------------------" << std::endl;
    std::cout << " 1) Play Lotto "             << std::endl;
    std::cout << " Q) Quit Program "           << std::endl;
    std::cout << "Please make a selection: ";
    char choice;
    std::cin >> choice;

    switch(choice)
    {
        case '1':
            {
                std::cout << "\n Please enter your name: ";
                std::string name;
                std::cin  >> name;

                const ticket_t user    = getLottoPicks();
                const ticket_t winning = genWinNums();

                std::cout << "User ticket:    " << user    << "\n";
                std::cout << "Winning ticket: " << winning << "\n";

                // check win?
                bool ok = 0 == std::lexicographical_compare(
                        user.begin(), user.end(),
                        winning.begin(), winning.end());

                std::cout << "Result of draw: " << (ok? "WINNER":"No luck") << "\n";
            }
        case 'Q': case 'q':
            return 0;
        default:
            std::cout << "\n That is not a valid choice." << std::endl;
    }

    std::cin.ignore(1<<24,'\n');
    std::cout << "\n Press enter...";
    std::string dummy;
    std::getline(std::cin, dummy);
}

WildCrustacean · Accepted Answer · 2012-11-16T23:47:08.523

1

Looks like you are never assigning any values to the WinningNums array in your routine, that might explain why you get the same number all the time.

I'd suggest removing the numbers array and working directly with WinningNums to generate your random numbers.

edited Nov 16 '12 at 23:47

answered Nov 16 '12 at 23:30

WildCrustacean

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The GenWinNums generates 7 random numbers between 1 and 40. The other 2 loops you see that are confusing you just make sure there are no duplicates and that they are not higher than 40 and less than 1. – n0de Nov 16 '12 at 23:34
Is the `WinningNums[]` argument supposed to contain the 7 random numbers after you compute them? – WildCrustacean Nov 16 '12 at 23:37
Yes exactly, it is supposed to contain the 7 numbers generated. – n0de Nov 16 '12 at 23:40
Ok, then at some point you would need to assign to the elements of that array, i.e. `WinningNums[i] = numbers[i]`, or just get rid of the `numbers` array and work directly with the `WinningNums` argument – WildCrustacean Nov 16 '12 at 23:45

Passing Arrays into Functions in C++? [Lottery Numbers]

2 Answers2

More typical C++ solution