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POC++ int array pointers recursively to find prime factors
 

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  1. POC++ int array pointers recursively to find prime factors
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    <p>I am trying to make a function that can return the prime factors of a given number in an array (or multi-set, but I'm trying to use an array).</p> <p>For example, if I put in 12, I want to get 2, 2, and 3, not 2, and 3 like with a set. This is so that I can use these to see if it is a <a href="http://en.wikipedia.org/wiki/Smith_number" rel="nofollow">Smith number</a> or not, so I need the numbers seperately.</p> <p>Also, I am taking a recursive approach.</p> <p>I have tried (to no avail) to return the array many ways, including passing an initial pointer into the code which points to a space to store the array.</p> <p>I've tried just initializing the array in the function and then returning it.</p> <p>From what I can tell, I can get the array back from the base case iteration and then when trying to construct a new array with size <code>oldArray+1</code> to copy values to, things get messy. This is where I get lost.</p> <p>From what I've read, although this isn't the most efficient implementation, I should be able to make it work.</p> <p>I have a function, <code>nextPrime(int n)</code>, which given <code>n</code> will give back the next prime up from that number.</p> <p>See source below:</p> <pre><code>int* find(int n, int p) { int root = (int) floor(sqrt(n)); if (p &gt; root) { // Base case, array gets initialized and returned // depending on value of n and p. if (n &gt; 1) { factors = new int[1]; factors[0] = n; return factors; } else { factors = new int[0]; return factors; } } else if (n%p == 0){ // Inductive step if p is a factor int newFloor = (int) floor(n/p); factors = find(newFloor, p); // Initialize new array. int* newFactors; newFactors = new int[(sizeof(factors) / sizeof(int)) + 1]; // Add p to first slot, fill rest with contents of factors. factors[0] = p; for (int i = 0; i &lt; (sizeof(factors) / sizeof(int)); i++) { newFactors[i+1] = factors[i]; } return newFactors; } else { // Inductive step p isn't a factor of n factors = find(n, factors, nextPrime(p)); return factors; } } </code></pre> <p>As I say, the error is with returning the array and using its value, but why does it seem to return OK from the first iteration?</p>
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