Need help to avoid using a global array variable

[random++]

Hi all, this is my first post :-) I am learning C++ and I would really appreciate your help.

I wrote a small program that generates random combinations of lottery numbers, and which can be adapted to different types of lotteries.

The problem I am trying to solve is that, as you can see, I have used an array as a global variable.

If this wasn't an array, I would know how to use either pointers or references to avoid a global variable. However, I am not sure how to do this with an array.

Many thanks in advance -- any help or input will be greatly appreciated!

/* Generate combinations of lottery numbers */

#include <algorithm>	// for sort()
#include <conio.h>	// for getch()
#include <iostream>
#include <time.h>	// for time()

using namespace std;

int const HOW_MANY = 5;			// set how many numbers are returned each time
int const CEILING = 90;			// set the highest number that can be returned
int numbers[HOW_MANY] = {0};		// array containing the main numbers

int randomize(int max) {		// return a random number between 1 and max
	return rand() &#37; max + 1;
}

void doNumbers() {
	int i;
	for (i=0; i<HOW_MANY; i++)
		numbers[i] = randomize(CEILING);	// call randomize() HOW_MANY times to generate the combination
	sort(numbers, numbers+HOW_MANY);		// sort the combination
	for (i=0; i<(HOW_MANY-1); i++)
		if (numbers[i] == numbers[i+1])		// compare each number with the next one
			doNumbers();			// if there are any duplicates, repeat the function
}

void printNumbers() {
	int i;
	for (i=0; i<HOW_MANY; i++)
		cout << numbers[i] << "\t";
}

void giveOptions() {
	cout << "\n\nWould you like one more combination?\n\n";
	cout << "- Enter Y for YES\n";
	cout << "- Enter N to end the program" << "\n\n\n";
	int _getch();
	switch (_getch()) {
		case 'y':
		case 'Y':
			doNumbers();
			printNumbers();
			giveOptions();
			break;
		case 'n':
		case 'N':
			return;
		default:
			cout << "\n\nPlease enter either Y or N\n\n\n";
			giveOptions();
	}
}

int main() {
	srand(unsigned(time(NULL)));
	doNumbers();
	printNumbers();
	giveOptions();
	return 0;
}

[Lindley]

The name of an array may be interpreted as a pointer to the first element of the array. Does that help?

[random++]

Thanks Lindley,

I tried to use the array name as if it were a pointer, but I got all sorts of compiler errors. As you can see, the code not only assigns a value to each element of the array, but it also sorts the values, and checks for duplicates.

I am probably missing something obvious, but I am not sure of which exact syntax should be used in the function doNumbers() in case I were to create a local array instead than a global one.

[random++]

I also tried creating an array on the free store:

int *numbers = new int[5];

...but then I didn't know how to refer to it from within another function: whatever syntax I use, I get an "undeclared identifier" compile-time error.

What am I missing?

[Mybowlcut]

So you want to know how to pass arrays to functions?

void f(int* numbers, size_t size)
{
    for(size_t i = 0; i < size; ++i)
    {
        std::cout << numbers[i] << std::endl;
    }
}

int main()
{
    const int QTY = 5;
    int numbers[QTY] = {10, 20, 30, 40, 50};  
    f(numbers, QTY);

    return 0;
}

If this wasn't an array

Does it have to be an array? A vector is a lot more convenient.

[Lindley]

Thanks Lindley,

I tried to use the array name as if it were a pointer, but I got all sorts of compiler errors.

Such as? Show both the attempted code and the result.

[random++]

So you want to know how to pass arrays to functions?

Thank you SO much! I finally know what I was missing -- I have fixed the code as per your suggestion and it works perfectly!

/* Generate combinations of lottery numbers */

#include <algorithm>	// for sort()
#include <conio.h>	// for getch()
#include <iostream>
#include <time.h>	// for time()

using namespace std;

int const SIZE = 5;			// set how many numbers are returned each time
int const CEILING = 90;			// set the highest number that can be returned

void doNumbers(int *numbers, int SIZE);
void printNumbers(int *numbers);
void giveOptions(int *numbers, int SIZE);

int main() {
	int numbers[SIZE] = {0};
	srand(unsigned(time(NULL)));
	doNumbers(numbers, SIZE);
	printNumbers(numbers);
	giveOptions(numbers, SIZE);
	return 0;
}

int randomize(int max) {		// return a random number between 1 and max
	return rand() % max + 1;
}

void doNumbers(int *numbers, int SIZE) {
	for (int i=0; i<SIZE; i++)
		numbers[i] = randomize(CEILING);	// call randomize() SIZE times to generate the combination
	sort(numbers, numbers+SIZE);		// sort the combination
	for (int i=0; i<(SIZE-1); i++)
		if (numbers[i] == numbers[i+1])		// compare each number with the next one
			doNumbers(numbers, SIZE);					// if there are any duplicates, repeat the function
}

void printNumbers(int *numbers) {
	for (int i=0; i<SIZE; i++)
		cout << numbers[i] << "\t";
}

void giveOptions(int *numbers, int SIZE) {
	cout << "\n\nWould you like one more combination?\n\n";
	cout << "- Enter Y for YES\n";
	cout << "- Enter N to end the program" << "\n\n\n";
	int _getch();
	switch (_getch()) {
		case 'y':
		case 'Y':
			doNumbers(numbers, SIZE);
			printNumbers(numbers);
			giveOptions(numbers, SIZE);
			break;
		case 'n':
		case 'N':
			return;
		default:
			cout << "\n\nPlease enter either Y or N\n\n\n";
			giveOptions(numbers, SIZE);
	}
}

Does it have to be an array? A vector is a lot more convenient.

I know -- thanks. That's actually my next goal: to re-write the same program using vectors. After that, I'll try to re-write it using classes as well. This will help me learn

Thanks again!

[random++]

Such as? Show both the attempted code and the result.

The error was "undeclared identifier".

What I was doing wrong (I now realized) is that, after creating the array within one function, I was trying to use it in another function without passing it in as an argument. Newbie mistake

Thanks a lot for your help!