prime printing

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
#include <ext/pb_ds/assoc_container.hpp>
using namespace __gnu_pbds;
typedef tree<ll,null_type,less_equal<ll>,rb_tree_tag,tree_order_statistics_node_update>ordered_set;
#define suni ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0)
#define endl "\n"
#define mn int main()
#define frac() cout.unsetf(ios::floatfield);cout.precision(6);cout.setf(ios::fixed,ios::floatfield);

/*const int mx=1e6+123;
bool isprime[mx];
vector<int>prime;
void primegen(int n)
{
    memset(isprime, 1,sizeof(isprime));
    isprime[1]=0;
    for(int i=2;i<=n;i++){
        for(int j=i*2;j<=n;j+=i)   //O(n*ln(n))
            isprime[j]=0;
    }
    for(int i=2;i<=n;i++){
        if (isprime[i]) prime.push_back(i);
    }
}

mn
{
    suni;
    int n; cin>>n;
    primegen(n);
    for(auto u:prime) cout<<u<<" ";
    cout<<endl;
}*/


/*const int mx=1e6+123;
bool isprime[mx];
vector<int>prime;
void primegen(int n)
{
    memset(isprime, 1,sizeof(isprime));
    isprime[1]=0;
    for(int i=2;i<=n;i++){
            if(isprime[i]){
        for(int j=i*2;j<=n;j+=i)
            isprime[j]=0;
      }
    }
    for(int i=2;i<=n;i++){
        if (isprime[i]) prime.push_back(i);
    }
}

mn
{
    suni;
    int n; cin>>n;
    primegen(n);
    for(auto u:prime) cout<<u<<" ";
    cout<<endl;
}*/

/*const int mx=1e6+123;
bool isprime[mx];
vector<int>prime;
void primegen(int n)
{
    memset(isprime, 1,sizeof(isprime));
    isprime[1]=0;
    for(int i=3;i<=n;i+=2){
            if(isprime[i]){
        for(int j=i*2;j<=n;j+=i)
            isprime[j]=0;
      }
    }
    prime.push_back(2);
    for(int i=3;i<=n;i+=2){
        if (isprime[i]) prime.push_back(i);
    }
}

mn
{
    suni;
    int n; cin>>n;
    primegen(n);
    for(auto u:prime) cout<<u<<" ";
    cout<<endl;
}*/


//seieve algo of generating prime
const int mx=1e8+123;
bool isprime[mx];
vector<int>prime;
void primegen(int n)
{
   for(int i=3;i<=n;i+=2) isprime[i]=1;
    for(int i=3;i*i<=n;i+=2){
            if(isprime[i]){
        for(int j=i*i;j<=n;j+=(i*2))
            isprime[j]=0;
      }
    }
    isprime[2]=1;
    prime.push_back(2);
    for(int i=3;i<=n;i+=2){
        if (isprime[i]) prime.push_back(i);
    }
}

mn
{
    suni;
    primegen(1e8);
    for(int i=0;i<prime.size();i+=100) cout<<prime[i]<<endl;
}