Language: C++

#include <bits/stdc++.h>
#define mod 1000000007
#define pb emplace_back
#define dbg(x) cout << #x << ": " << x << endl
#define check(k, i, j) ((k>=i) && (k<=j))
#define FAST_IO ios_base::sync_with_stdio(false), cin.tie(NULL), cout.tie(NULL)
typedef long long ll;
using namespace std;
int dx[]={1,1,0,-1,-1,-1, 0, 1}; 
int dy[]={0,1,1, 1, 0,-1,-1,-1};

template<typename T>
void printV(vector<T> v){
    for(int i=0; i<v.size(); i++){
        cout << v[i]%mod << " ";
    }
    cout << endl;
}

template<typename T>
void printA(T arr[], ll n){
    for(int i=0; i<n; i++){
        cout << arr[i] << " ";
    }
    cout << endl;
}

template<typename T>
void printPA(T* arr, ll n){
    for(int i=0; i<n; i++){
        cout << arr[i] << " ";
    }
    cout << endl;
}

// ===================================== //

int main(){

    #ifndef ONLINE_JUDGE
        freopen("input.txt", "r", stdin); 
        freopen("output.txt", "w", stdout);
    #endif 

    FAST_IO;
    int x;
    cin >> x;
    cout << ((x>=30) ? "YES" : "NO") << endl; 

    return 0;
}
#include <bits/stdc++.h>
#define mod 1000000007
#define pb emplace_back
#define dbg(x) cout << #x << ": " << x << endl
#define check(k, i, j) ((k>=i) && (k<=j))
#define FAST_IO ios_base::sync_with_stdio(false), cin.tie(NULL), cout.tie(NULL)
typedef long long ll;
using namespace std;
int dx[]={1,1,0,-1,-1,-1, 0, 1}; 
int dy[]={0,1,1, 1, 0,-1,-1,-1};

template<typename T>
void printV(vector<T> v){
    for(int i=0; i<v.size(); i++){
        cout << v[i]%mod << " ";
    }
    cout << endl;
}

template<typename T>
void printA(T arr[], ll n){
    for(int i=0; i<n; i++){
        cout << arr[i] << " ";
    }
    cout << endl;
}

template<typename T>
void printPA(T* arr, ll n){
    for(int i=0; i<n; i++){
        cout << arr[i] << " ";
    }
    cout << endl;
}

// ===================================== //

int main(){



    FAST_IO;
    int x;
    cin >> x;
    cout << ((x>=30) ? "YES" : "NO") << endl; 

    return 0;
}


Compiler output:
a.cc:60:5: error: redefinition of 'int dx []'
   60 | int dx[]={1,1,0,-1,-1,-1, 0, 1};
      |     ^~
a.cc:9:5: note: 'int dx [8]' previously defined here
    9 | int dx[]={1,1,0,-1,-1,-1, 0, 1};
      |     ^~
a.cc:61:5: error: redefinition of 'int dy []'
   61 | int dy[]={0,1,1, 1, 0,-1,-1,-1};
      |     ^~
a.cc:10:5: note: 'int dy [8]' previously defined here
   10 | int dy[]={0,1,1, 1, 0,-1,-1,-1};
      |     ^~
a.cc:64:6: error: redefinition of 'template<class T> void printV(std::vector<_Tp>)'
   64 | void printV(vector<T> v){
      |      ^~~~~~
a.cc:13:6: note: 'template<class T> void printV(std::vector<_Tp>)' previously declared here
   13 | void printV(vector<T> v){
      |      ^~~~~~
a.cc:72:6: error: redefinition of 'template<class T> void printA(T*, ll)'
   72 | void printA(T arr[], ll n){
      |      ^~~~~~
a.cc:21:6: note: 'template<class T> void printA(T*, ll)' previously declared here
   21 | void printA(T arr[], ll n){
      |      ^~~~~~
a.cc:80:6: error: redefinition of 'template<class T> void printPA(T*, ll)'
   80 | void printPA(T* arr, ll n){
      |      ^~~~~~~
a.cc:29:6: note: 'template<class T> void printPA(T*, ll)' previously declared here
   29 | void printPA(T* arr, ll n){
      |      ^~~~~~~
a.cc:89:5: error: redefinition of 'int main()'
   89 | int main(){
      |     ^~~~
a.cc:38:5: note: 'int main()' previously defined here
   38 | int main(){
      |     ^~~~