Twin Prime Numbers between 1 and n | C ++ program print all twin primes using Sieve of Eratosthenes . ; Create a boolean array " prime [ 0 . . n ] " and initialize all entries it as true . A value in prime [ i ] will finally be false if i is Not a prime , else true . ; If prime [ p ] is not changed , then it is a prime ; Update all multiples of p ; to check for twin prime numbers display the twin primes ; Driver Program to test above function ; Calling the function
#include <bits/stdc++.h> NEW_LINE using namespace std ; void printTwinPrime ( int n ) { bool prime [ n + 1 ] ; memset ( prime , true , sizeof ( prime ) ) ; for ( int p = 2 ; p * p <= n ; p ++ ) { if ( prime [ p ] == true ) { for ( int i = p * 2 ; i <= n ; i += p ) prime [ i ] = false ; } } for ( int p = 2 ; p <= n - 2 ; p ++ ) if ( prime [ p ] && prime [ p + 2 ] ) cout << " ( " << p << " , ▁ " << p + 2 << " ) " ; } int main ( ) { int n = 25 ; printTwinPrime ( n ) ; return 0 ; }