Alex's exercise Chapter 6 Ex3

Code:

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/*Design a program that finds all numbers from 1 to 1000 whose prime factors, when added
together, sum up to a prime number (for example, 12 has prime factors of 2, 2, and 3, which
sum to 7, which is prime). Implement the code for that algorithm.*/

#include <iostream>

using namespace std;

int primes(int n);
bool isPrime(int divisor);
bool check(int result);

int main()
{

    // Check numbers from 1 to 1000
    for (int i = 2; i <= 1000; ++i)
    {
        int result = primes(i);

        if (check(result))
        {
            cout << i << endl;
        }
    }
}

bool isPrime(int divisor)
{
    for (int j = 2; j <= divisor/2; j++)
    {
        if (divisor % j == 0)
            return false;
    }
    return true;
}

int primes(int i)
{
    int p = i;
    int divisor = 2;

    int sum = 0;

    while (p != 1)
    {
        cout << "p: " << p << endl;
        cout << "le divisor: " << divisor << endl;
        if (isPrime(divisor))
        {
            if (p % divisor == 0)
            {
                p = p / divisor;
                sum += divisor;
            }
            else
            {
                divisor += 1;
            }
        }

    }



    return sum;
}

bool check(int result)
{
    for (int i = 2; i <= result / 2; i++)
    {
        if (result % i == 0)
            return false;
    }
    return true;
}

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My code does not do what is asked.

Could anyone check it up?

Define "does not do"

Quote:

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Originally Posted by Shakti

Define "does not do"

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The program should print numbers whose factors sum up to prime numbers. However, there is something wrong with int primes(n) function.

I get into infinite loop and print statements show that p : 5 and divisor : 4 and it stays like that in that loop. I cannot find a flaw in my logic.

Quote:

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Originally Posted by Valentas

The program should print numbers whose factors sum up to prime numbers. However, there is something wrong with int primes(n) function.

I get into infinite loop and print statements show that p : 5 and divisor : 4 and it stays like that in that loop. I cannot find a flaw in my logic.

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Use a debugger like gdb or what's built in to you IDE to step through loop, and verify what each variable each iteration. If you have a logic error, this will find it.