Euler function and finding Euler function by linear sieve

#include <iostream>
#include <cstring>
#include <algorithm>
using namespace std;
int phi(int x)
{
    
    int res = x;
    for (int i=2;i<=x/i;i++)
    {
    
        if (x%i==0)
        {
    
            res = res/i*(i-1);
            while (x%i==0) x/=i;
        }
    }
    if (x>1)  res = res/x*(x-1);
    return res;
}
int main()
{
    
    ios::sync_with_stdio(false);
    int n;
    cin>>n;
    while (n -- ){
    
        int x;
        cin>>x;
        cout<<phi(x)<<endl;
    }
    return 0;
}

Finding Euler function through linear sieve

#include <iostream>
#include <cstring>
#include <algorithm>
using namespace std;
typedef long long LL;
const int N = 1e6+10;
int pri[N],cnt,phi[N];
bool st[N];
void cul_phi(int n)
{
    
    phi[1]=1;
    for (int i=2;i<=n;i++)
    {
    
        
        if (!st[i]) {
    
            phi[i] = i-1;  
            pri[cnt++] = i;
        }
        for (int j=0;pri[j]<=n/i;j++)
        {
    
            int t = pri[j]*i;
            st[t] = true;
            if (i%pri[j]==0){
    
                phi[t] = phi[i]*pri[j];
                break;
            }
            phi[t] = phi[i]*(pri[j]-1);
        }
        
    }
}
int main()
{
    
    int n;
    LL sum=0;
    scanf("%d", &n);
    cul_phi(n);
    for (int i=1;i<=n;i++) sum+=phi[i];
    printf ("%lld\n",sum);
    return 0;
}