Print prime numbers from 1 to N in reverse order | C ++ program to print all primes between 1 to N in reverse order 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 ; Print all prime numbers in reverse order ; Driver Program ; static input ; to display ; Reverseorder ( N ) ; calling the function
#include <bits/stdc++.h> NEW_LINE using namespace std ; void Reverseorder ( 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 = n ; p >= 2 ; p -- ) if ( prime [ p ] ) cout << p << " ▁ " ; } int main ( ) { int N = 25 ; cout << " Prime ▁ number ▁ in ▁ reverse ▁ order " << endl ; if ( N == 1 ) cout << " No ▁ prime ▁ no ▁ exist ▁ in ▁ this ▁ range " ; else return 0 ; }