Write a program that finds and prints all of the prime numbers between 3 and n.

Question

Write a program that finds and prints all of the prime numbers between 3 and n. The program should allow the user to input n. A prime number is a number such that 1 and itself are the only numbers that evenly divide it (for example, 3, 5, 7, 11, 13, 17, …).
One way to solve this problem is to use a doubly nested loop. The outer loop can iterate from 3 to n while the inner loop checks to see if the counter value for the outer loop is prime. One way to see if number m is prime is to loop from 2 to m – 1 and if any of these numbers evenly divides m, then m cannot be prime. (Note that there are several ways to make this algorithm more efficient.)

//Header files
#include<iostream>
using namespace std; int main()

{

Explanation / Answer

#include <iostream>
using namespace std;
int main ()
{
int prime;
int n;
cout << "Enter a number bigger than 3" << endl;
cin >> n; //

if(n < 3)
   cout << "INVALID ENTRY" << endl;
else
{
   for(prime=3; prime <= n; prime= prime+2)//even# are never prime
   {

      for(int count=2; count < prime; count++)//checking if #is prime
      {
         if(prime % count > 0 and count == prime-1 ) //if remainder zero
         cout << prime << " is a prime number" << endl;
         else if(prime % count == 0)//if remainder=zero endloop
         count = prime;
      }
   }
}
}

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