Test for prime by checking for divisibility by all whole numbers from 2 to sqrt(n). - C++ Data Type

C++ examples for Data Type:int

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Description

Test for prime by checking for divisibility by all whole numbers from 2 to sqrt(n).

Demo Code

#include <iostream>
#include <cmath>
using namespace std;
int main() {/*from   w w  w.  j  a  v  a2s .  com*/
   int  n = 0;  // Number to test for prime-ness
   int  i = 2;  // Loop counter
   bool is_prime = true;   // Boolean flag...
   // Assume true for now.
   // Get a number from the keyboard.
   cout << "Enter a number and press ENTER: ";
   cin >> n;
   // Test for prime by checking for divisibility by all whole numbers from 2 to sqrt(n).
   while (i <= sqrt(n)) {
      if (n % i == 0) {           //  If i divides n,
         is_prime = false;  //    n is not prime.
      }
      ++i;                        //  Add 1 to i.
   }
   // Print results
   if (is_prime) {
      cout << "Number is prime." << endl;
   } else {
      cout << "Number is not prime." << endl;
   }
   return 0;
}

Result


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