Welcome to the Treehouse Community

Want to collaborate on code errors? Have bugs you need feedback on? Looking for an extra set of eyes on your latest project? Get support with fellow developers, designers, and programmers of all backgrounds and skill levels here with the Treehouse Community! While you're at it, check out some resources Treehouse students have shared here.

Looking to learn something new?

Treehouse offers a seven day free trial for new students. Get access to thousands of hours of content and join thousands of Treehouse students and alumni in the community today.

Start your free trial

C#

andrewgabriel
andrewgabriel
18,106 Points
Posted by andrewgabriel
andrewgabriel
18,106 Points

Prime number program issue

I am trying to create a program to take any user input and calculate to see whether it's prime or not and return 0 or 1. 1 would be true and 0 false. I got the main core of the program written and it does work however when I wrap it with while (cin >> n) so that it keeps going as long as there is a prompt to enter a value from the user, it starts getting random and returning inaccurate results. I am writing this in C++ however it's pretty similar concept to C# or any language. Here is my code:

int main() {
    int n; // initialize variable for user input
    bool isPrime = true; // initialize variable for prime state
    cin >> n;

    while (cin >> n) {
        if (n == 1) {
            isPrime = false;
            break;
        }
        for (int i = 2; i <= n/2; i++) {
            if (n % i == 0) {
                isPrime = false;
                break;
            }
        }
        cout << isPrime << "\n";

    }
    return 0;
}
Steven Parker
Steven Parker
231,198 Points
Steven Parker
Steven Parker
231,198 Points

What size number are you using? Are you exceeding integer precision?

andrewgabriel
andrewgabriel
18,106 Points
andrewgabriel
andrewgabriel
18,106 Points

Steven Parker The numbers I am using are between 1 to maybe 1000 nothing too crazy to potentially introduce any confusion in the program

1 Answer

Steven Parker
Steven Parker
231,198 Points
Steven Parker
Steven Parker
231,198 Points

You need to reset isPrime each time you begin the loop.

Since you initialilze isPrime outside the loop, once you get a False result, all other results will be False. You need to reset it to True as the loop begins again.

Jason Anello
Jason Anello
Courses Plus Student 94,610 Points

1 is not a prime number.

Steven Parker
Steven Parker
231,198 Points
Steven Parker
Steven Parker
231,198 Points

I guess it's excluded by definition. It's easy to get confused because it meets the criteria of having "only whole-number factors are 1 and itself".