Question

For C++:

a) Write a function is_prime that takes a positive integer X and returns 1 if X is a prime number, or 1 if X is not a prime number.

b) write a program that takes a positive integer N and prints all prime numbers from 2 to N by calling your function is_prime from part a.

Answer 1

#include <iostream>

using namespace std;

int is_prime(int num)
{
   int i;
   if (num <= 1) return 0;
   if (num % 2 == 0 && num > 2) return 0;
   for (i = 3; i < num / 2; i += 2)
   {
      if (num % i == 0)
         return 0;
   }
   return 1;
}

int main(){
   int n;
   cout<<"Enter a number: ";
   cin>>n;
   cout<<"Primes from 2 to "<<n<<" are:"<<endl;
   for(int i = 2;i<=n;i++){
      if(is_prime(i)){
         cout<<i<<endl; 
      }
   }
   return 0;
}