Question

Hi there i’m trying to make a function in C++ that takes a number, i, and decides if it is a prime number or not by running through a loop to find it’s multiples, and then makes sure it isn’t prime through a series of test. However, it seems the loop isn’t even being run through. I’ve told it to output no matter where in the loop it is, but I get no outputs. Here is the code:

#include <iostream>

using namespace std;

int main()
{
    int j =1;
    int z = 0;
    int i = 10;
    bool p = false;
    while (p = false){
        cout << "not starting ifs";
        z=i%j;
        if (z==0 && j>2){
        p=true;
        cout << "not prime" << endl << "loops to if";
        }
        else if (j==1){
            j++;
            cout <<"loops to else if 1";
            }
        else if ( i==2 || j==i ){
          p = true;
          cout << "prime" << endl << "loops to else if 2";
            }
            else {
            j++;
            cout << "loops to else";
                }
        }
            return 0;
}

I don’t care whether or not the math behind it is right, I want to figure that out myself for the learning experience. But if anyone could help me figure this out with a good easy to understand explanation I would appreciate it! I”m really new to programming, so I’m not used to jargon yet. I look forward to your advice!

Answer 1

You are using = instead of == in

while (p = false){

When you do that, you assign false to p and the result of the expression is false which gets tested in the while loop resulting in exiting of the loop.