ex75122.cpp

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/**************************************************************************
PURPOSE:   decide whether a number is a <prime number> or not
TIME: 08/10/25
AUTHOR:   ch8_daniel
INPUT:   num
        an integer number
OUTPUT: It may be ">>It's a prime number." or ">>It's not a prime number."
VERSION:   1.0
**************************************************************************/

#include <iostream>

#include <cmath>

using namespace std;
int main()
{
   int num;
   int snum;   // sqrt(num)

   cout << "Enter a integer number:";
   cin >> num;

   snum = sqrt(num);

   for (int i=2; i<snum+1; i++)
   {
       if (num%i == 0)
       {
           cout << ">>It's not prime number.";
           return 0;
       }
   }

   cout << ">>It's a prime number.";

return 0;
}