Question

I am wondering I can get some help at debugging or spotting the error in my program. The objective is to obtain user input and then display primes from input to zero, greatest prime to lowest.

Problem is the output includes the user input which may or may not be a prime number in itself, and repeats primes several times 🙁
Also, I am wondering why 2 isn’t included?

My code:

#include <iostream>
#include <cmath>
using namespace std;

int main()
{
    int prime, division, input;
    cout << "Please enter a number you wish to count down prime numbers from." << endl;
    cin >> input;

    for (prime = input ; prime >=2 ; prime-- )
    {
        for (division = 2 ; division < prime ; division++ )
        {
            if (prime % division == 0)
            {
            break;
            }
            else
            {
            cout << prime << " ";
            }
        }
    }
    return 0;
}

My output:

Please enter a number you wish to count down prime numbers from.
15

15 13 13 13 13 13 13 13 13 13 13 13 11 11 11 11 11 11 11 11 11 9 7 7 7 7 7 5 5 5 3

Thanks for those who help!

Answer 1

Try this code

#include <iostream>
#include <cmath>
using namespace std;

int main()
{
    int prime, division, input;
    cout << "Please enter a number you wish to count down prime numbers from." << endl;
    cin >> input;




    for (prime = input ; prime >=2 ; prime--)
    {
        boolean isDivisible = false;
        for (division = 2 ; division < prime ; division ++)
        {
            if (prime % division == 0)
            {
                isDivisible = true;
            }
        }
        if (isDivisible == false)
        {
            cout << prime << " ";
        }
    }
    return 0;
}