Locker Puzzle, help.

[EMetalmulishaH]

Problem for puzzle:
A high school has 1000 students and 1000 lockers, one locker for each student. On the first day of school the principal plays the following game: She asks the first student to go and open all the lockers. She then asks the second student to go and close all the even-numbered lockers. The third student is asked to check every third locker. If it is open, the student closes it; if it is closed, the student opens it. The fourth student is asked to check every fourth locker. If it is open, the student closes it; if it is closed, the student opens it. The remaining students continue this game. In general, the nth student checks every nth locker. If the locker is open, the student closes it; if it is closed the student opens it. After all the students have taken their turn, some of the lockers are open and some are closed.

Write a program that prompts the user to enter the number of lockers in a school. After the game is over, the program outputs the number of lockers that are opened. Test run your program for the following inputs: 1000, 5000, 100000.

The problem I am having is not having an expanding array I think. I could set the array to 10,001, but that would not work for higher numbers. The class I am in is C++ 101, we have not even touched on arrays yet, I am taking the class as a refresher course so I understand a little about them, and figured using an array is my best option. Can any one give me some advice on how to set up an expanding array in this problem?

#include "stdafx.h"
#include <iostream>
using namespace std;

int main()
{
	int lockers[1001];
	int numLockers;
	int openLockers;
	cout << "Please enter the number of Lockers. " << endl;
	cin >> numLockers;

	for (int i = 1; i <= numLockers; i++)
	{
		lockers[i] = 0;
	}
	for (int i = 1; i <= numLockers; i++)
	{
		for (int j = 1; j <= numLockers; j++)
		{
			if (j % i == 0)
			{
				lockers[j] = 1 - lockers[j];
				openLockers = 0;
			}
		}
	}
	for (int i = 1; i <= numLockers; i++)
	{
		openLockers += lockers[i];
	}

	cout << "The number of lockers open are " << openLockers << "." <<  endl;

	return 0;
}

[TheKingOfTyrants]

Sounds like you need to dynamically allocate memory based on the user's input. I'd recommend using the new operator. Example:

int numLockers;
int openLockers;
cout << "Please enter the number of Lockers. " << endl;
cin >> numLockers;
int *lockers = new int[ numLockers ];

For there, you can access every element in this new array the same you you always have.

As a side note, I'd recommend using a bool type for the lockers variable because the state of the locker is a binary choice: open or closed.

[mlholder]

It may not give you any issues, but on lines 13 - 16, you initialize lockers[1] to lockers[numLockers], but not lockers[0]. Array indexing always starts at 0, thus lockers[0] = some garbage value. As for expanding arrays, you might want to look into using a vector.

[anup30]

//gcc and clang compiler allows you this way...
//visual studio dont
#include <iostream>
using namespace std;

int main()
{
    int n;
    cout << "input array size: ";
    cin >> n; // woked for n= 100,000 in  http://cpp.sh/
    int array[n];
    
    for(int i=0; i<n; i++ )       
        array[i] = i*2;            
       
    for(int i=0, k=0; i<n; i++ ) // print
    { 
      cout << array[i] << "\t"; 
      k++; 
      if(k%10 ==0) // 10 column
      {cout << "\n"; k=0;} 
    }     
	
return 0;
}