I am supposed to augment the code below. Im supposed to use a change the program

Question

I am supposed to augment the code below. Im supposed to use a change the program so that i use a VECTOR instead of an array.

Im not sure how to to this.

Code follows below.

#include <bits/stdc++.h>

using namespace std;

void SieveOfEratosthenes(int n)

{

    // Create a boolean array "prime[0..n]" and initialize

    // all entries it as true. A value in prime[i] will

    // finally be false if i is Not a prime, else true.

    bool prime[n+1];

    memset(prime, true, sizeof(prime));

    for (int p=2; p*p<=n; p++)

    {

        // If prime[p] is not changed, then it is a prime

        if (prime[p] == true)

        {

            // Update all multiples of p

            for (int i=p*2; i<=n; i += p)

                prime[i] = false;

        }

    }

    // Print all prime numbers

    for (int p=2; p<=n; p++)

       if (prime[p])

          cout << p << " ";

}

// Driver Program to test above function

int main()

{

    int n = 30;

    cout << "Following are the prime numbers smaller "

         << " than or equal to " << n << endl;

    SieveOfEratosthenes(n);

    return 0;

}

Explanation / Answer

First, it makes sense to define an isPrime() function to make your code more readable:

bool isPrime(int p)
{
for(int i = 2; i <= p/2; i++)
{
if(p%i == 0)
{
return false;
}
}
return true;
}

Then you can write your main() in the following way:

int main()
{
int input;
cout << "Enter a positive integer: ";
cin >> input;

// You deal with integers here, so you shouldn't use vector<double>.
// As all numbers are positive, you could also use unsigned int.
vector<int> primeHolder;
for(int i = 2; i <= input; i++)
{
if(isPrime(i))
{
// If the tested value is a prime, append it to the vector.
primeHolder.push_back(i);
}
}

cout << "There are " << primeHolder.size() << " primes:" << endl;
for(size_t j = 0; j < primeHolder.size(); j++)
{
// Print every prime number that was stored in the vector.
cout << primeHolder[j] << endl;
}
return 0;
}

Below is the output as follows:

Enter a positive integer: 10
There are 4 primes:
2
3
5
7

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