Thread: Is it prime? Logic error

I've got a logic error in here and I am having trouble figuring it out.

Can someone please point out the obvious as I cannot see it.

Code:

#include <iostream>
#include <math.h>
using namespace std;

int main(){

    int i, n, squirt;
    bool is_prime = true;

    cout << "Enter a number: ";
    cin >> n;

    squirt = sqrt(static_cast<double>(n));

    for(i = 2; i <= squirt; i++){
        if(i % squirt == 0){
            is_prime = false;
            break;
        }
    }

    cout << n << " is ";
    if(!is_prime)
        cout << "not ";
    cout << "a prime number.";

    cout << endl;

    return 0;
}

TIA!

Originally Posted by oogabooga

Look carefully at line 16.

Thanks!

Originally Posted by oogabooga

It's completely out-to-lunch.

Not sure what this means.

Referring to previously working code, I fixed it with this:

Code:

#include <iostream>
#include <math.h>
using namespace std;

int main(){

    int i, n, squirt;
    bool is_prime = true;

    cout << "Enter a number: ";
    cin >> n;

    squirt = sqrt(static_cast<double>(n));

    for(i = 2; i <= squirt; i++){
        if(n % squirt == 0){
            is_prime = false;
            break;
        }
    }

    cout << n << " is ";
    if(!is_prime)
        cout << "not ";
    cout << "a prime number.";

    cout << endl;

    return 0;
}

Originally Posted by oogabooga

Line 16 is still wrong.

Hard to break it, but I did.

This doesn't seem to break:

Code:

#include <iostream>
#include <math.h>
using namespace std;

int main(){

    int i, n, squirt;
    bool is_prime = true;

    cout << "Enter a number: ";
    cin >> n;

    squirt = sqrt(static_cast<double>(n));

    for(i = 2; i <= squirt; i++){
        if(n % i == 0){
            is_prime = false;
            break;
        }
    }

    cout << n << " is ";
    if(!is_prime)
        cout << "not ";
    cout << "a prime number.";

    cout << endl;

    return 0;
}

Thanks for your assistance.