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[C++] Prime Number Test - Descriptions & Code
Descriptions & Code
===========< Descriptions >==============
-> VSC++ 2005 - Win32 Console App
-> Test to see is a number prime ?
It uses a simple mathematical algorithm :
"a non-prime number has at least a prime denominator, that is less than or equal to the square root of the number", and as an enhance : all even numbers except 2, aren't prime.
===========< Code >==============
#include <cmath> // sqrt()
#include <iostream> // system()
using namespace std;
int main()
{
int n; // n is prime ?
bool prime =true; // yes, is prime!
cout << "\n Enter a number : ";
cin >> n;
if ( (n%2 == 0 && n!=2) || (n == 1) ) // dividable by 2 (but not 2) or it's 1 ?
prime = false;
for (int i=3; i <= sqrt((double)n) && prime; i+=2)
if ( n%i == 0 )
prime = false;
if ( prime )
cout << "\n Number is prime." << endl;
else
cout << "\n Number isn't prime." << endl;
system("pause");
return 0;
}
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