Sieve Algorithm for finding Prime Numbers

Write a C++ program to print all the prime numbers which is less than the given number using sieve algorithm.

Program :

#include <cmath>

#include <cstdio>

#include <vector>

#include <iostream>

#include <algorithm>

using namespace std;

int main() {

    /* Enter your code here. Read input from STDIN. Print output to STDOUT */  

    int a;

    cin>>a;

    int v[a]={0};

    for(int i = 2; i*i<=a;i++)

    {

        if(v[i]==0)

        {

            for(int j = i*i; j <= a;)

            {

                v[j]=1;

                j = j+i;

            }

        }

    } 

    for(int i = 2;i < a; i++)

    {

        if(v[i]==0)

         cout<<i<<endl;

    }

    return 0;

}