Question

Write a program that finds and prints all of the prime numbers between 3 and X (X is input from the user). 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 (a loop inside another 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 n is prime is to loop from 2 to n-1 and if any of these numbers evenly divides n, then n cannot be prime. If none of the values from 2 to n-1 evenly divides n, then n must be prime.

Note: do not use break statements, jumps, and user defined functions.

also tell how many prime numbers are there from 2 to n.

the language to be used is c++

Answer 1

#include <iostream>

using namespace std;

int main(){
   int X,i,j,c;
   cin>>X;
   for(i=3;i<=X;i++){
       c = 0;
       for(j=1;j<=i;j++){
           if(i%j == 0)
               c = c+1;
       }
       if(c == 2)
           cout<<i<<" ";
   }
  
   return 0;
}

Output :

First line is input

second line number are outputs