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POWhat is causing a segmentation fault?
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  1. POWhat is causing a segmentation fault?
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    copied!<p>I have been attempting to write a program that will determine if a number is prime or not. I have based it off of the Sieve of Eratosthenes. Anyway, my program works for small numbers (15485863 works), but if I use large numbers (ex. 17485863) I receive a segmentation fault. I am using unsigned long longs and do not think I have surpassed their maximum value. I just don't see what I have done wrong. Thank you in advance for any assistance!</p> <pre><code>#include &lt;iostream&gt; #include &lt;limits&gt; using namespace std; bool soe (unsigned long long); int main (void) { unsigned long long x = 17485863; bool q = soe(x); cout &lt;&lt; x &lt;&lt; " is "; if(q) cout &lt;&lt; "prime." &lt;&lt; endl; else cout &lt;&lt; "not prime." &lt;&lt; endl; return 0; } bool soe(unsigned long long input) { unsigned long long arrayLength = input%2 + input/2; unsigned long long index = 2; unsigned long long greatestMult = 0; bool array[arrayLength]; array[0] = true; //ignore true values in the array array[1] = true; do{ array[index] = false; }while(++index &lt; arrayLength); index = 2; do { if(input%index != 0) { greatestMult = input/index; while(index*greatestMult &gt; arrayLength) greatestMult--; do { array[index*greatestMult] = true; }while(--greatestMult &gt; 0); do { if(!array[index]) break; }while(++index &lt; arrayLength); } else { cout &lt;&lt; endl &lt;&lt; input &lt;&lt; " is divisble by " &lt;&lt; index &lt;&lt; endl; return false; } }while(index &lt; arrayLength); return true; } </code></pre>
 

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