Prime number program up to user defined number

[beginner24]

[Stewbond]

Your problem what that you initialized isPrime at the start of main() and never reset it. That meant that every number was not prime after the first non-prime number was detected. I fixed a few other things while I was at it, (most importantly indenting)

#include <iostream>
using namespace std;
int main ()
{
    int n=0; // Initialize to out of bounds lets you use 1 less line

    while (n <= 2)
    {
        cout << "Please enter a number greater than 2: " ; cin >> n;
    }

    for (int i=2; i<=n; ++i) //up to and including n
    {
        bool isPrime=true; // initialize for each test number, not only once per program

        for (int d=2; d<i; ++d)
            if (( i%d ) == 0)
            {
                isPrime=false;
                break;
            }
        if (isPrime==true)
        {
            cout << i << " Prime" << endl;
        }
    }
    return 0;
}

[beginner24]

Oh I see what you mean, no wonder only 2 and 3 came up since 4 isn't prime. This is my third program and still getting acquainted with formatting and everything. Thanks a lot for your help, Stewbond!

[Stewbond]

Another thing that I like to do is split things into functions so that you can understand what code is doing what.

int getValidInput()
{
    int n = 0;
    while (n <= 2)
    {
        cout << "Please enter a number greater than 2: ";
        cin >> n;
    }
    return n;
}

bool isPrime(int n)
{
    for (int d=2; d < i; ++d)
        if (i%d)
            return false;
    return true;
}

int main()
{
    int n = getValidInput();

    for (int i = 2; i <= n; ++i)
        if ( isPrime(i) )
            cout << i << " Prime" << endl;
    return 0;
}