criyle/codenet-compile-errors huggingface dataset:
Language: C++

#include<iostream>
#include<string>
using namespace std;
int main(){
  string s;
  cin>>s;
  int n=s.length()/2;
  for(i=0;i<n;i++){
    cout<<s.[2*i-1];
  }
}

Compiler output:
a.cc: In function 'int main()':
a.cc:8:7: error: 'i' was not declared in this scope
    8 |   for(i=0;i<n;i++){
      |       ^
a.cc:9:13: error: expected unqualified-id before '[' token
    9 |     cout<<s.[2*i-1];
      |             ^
Language: C++

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define rep(i, n) for(ll i = 0; i < (ll)(n); i++)
#define rep2(i, a, n) for(ll i = a; i < (ll)(n); i++)
#define memi cout << endl
#define kono(n) cout << fixed << setprecision(n)
#define all(c) (c).begin(), (c).end()
#define pb push_back
#define hina cout << ' '
#define in(n) cin >> n
#define in2(n, m) cin >> n >> m
#define in3(n, m, l) cin >> n >> m >> l
#define out(n) cout << n
const ll mei = (ll)1e9 + 7;

int main(){
  string s;
  in(s);
  for(ll i = 0, i < s.size(), i = i + 2ll){
    out(s[i]);
    if(i + 1 < s.size())
      out(s[i + 1]);
  }
  memi;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:20:18: error: expected ';' before '<' token
   20 |   for(ll i = 0, i < s.size(), i = i + 2ll){
      |                  ^~
      |                  ;
a.cc:20:19: error: expected primary-expression before '<' token
   20 |   for(ll i = 0, i < s.size(), i = i + 2ll){
      |                   ^
a.cc:20:42: error: expected ';' before ')' token
   20 |   for(ll i = 0, i < s.size(), i = i + 2ll){
      |                                          ^
      |                                          ;
Language: C++

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define rep(i, n) for(ll i = 0; i < (ll)(n); i++)
#define rep2(i, a, n) for(ll i = a; i < (ll)(n); i++)
#define memi cout << endl
#define kono(n) cout << fixed << setprecision(n)
#define all(c) (c).begin(), (c).end()
#define pb push_back
#define hina cout << ' '
#define in(n) cin >> n
#define in2(n, m) cin >> n >> m
#define in3(n, m, l) cin >> n >> m >> l
#define out(n) cout << n
const ll mei = (ll)1e9 + 7;

int main(){
  string s;
  in(s);
  for(ll i = 0; i < s.size(), i = i + 2ll){
    out(s[i]);
    if(i + 1 < s.size())
      out(s[i + 1]);
  }
  memi;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:20:42: error: expected ';' before ')' token
   20 |   for(ll i = 0; i < s.size(), i = i + 2ll){
      |                                          ^
      |                                          ;
Language: C++

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define rep(i, n) for(ll i = 0; i < (ll)(n); i++)
#define rep2(i, a, n) for(ll i = a; i < (ll)(n); i++)
#define memi cout << endl
#define kono(n) cout << fixed << setprecision(n)
#define all(c) (c).begin(), (c).end()
#define pb push_back
#define hina cout << ' '
#define in(n) cin >> n
#define in2(n, m) cin >> n >> m
#define in3(n, m, l) cin >> n >> m >> l
#define out(n) cout << n
const ll mei = (ll)1e9 + 7;

int main(){
  string s;
  in(s);
  for(ll i = 0; i < s.size(), i = i + 2){
    out(s[i]);
    if(i + 1 < s.size())
      out(s[i + 1]);
  }
  memi;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:20:40: error: expected ';' before ')' token
   20 |   for(ll i = 0; i < s.size(), i = i + 2){
      |                                        ^
      |                                        ;
Language: C++

#include <bits/stdc++.h>

#define all(v) v.begin(), v.end()
#define mp make_pair
#define EPS (int)1e-9
#define PI acos(-1)
#define endl '\n'
#define pb push_back
#define fi first
#define se second

using namespace std;
using ld = long double;
using ll = long long;
using vi = vector<int>;
using pii = pair<int, int>;

const int mod = 1000000007;


int main()
{
	ios_base::sync_with_stdio(0); cin.tie(0);
	string s;
	cin >> s;

	for(int i = 0; i < n; i+=2)
		cout << s[i];
	cout << endl;
	return 0;	
}

Compiler output:
a.cc: In function 'int main()':
a.cc:27:28: error: 'n' was not declared in this scope
   27 |         for(int i = 0; i < n; i+=2)
      |                            ^
Language: C++

#include <bits/stdc++.h>
using namespace std;

int main() {
    string s;
    cin >> s;
    for (int i = 1 i <= (int)s.size(); i++) {
        if (i%2 == 1) {
            cout << s[i];
        }
    }
    cout << endl;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:7:19: error: expected ';' before 'i'
    7 |     for (int i = 1 i <= (int)s.size(); i++) {
      |                   ^~
      |                   ;
Language: C++

#include <bits/stdc++.h>
using namespace std;

int main() {
  string s;
  cin >> s;
  string out(0);
  for (i = 0; i < s.size(); i+=2) {
    out += s.at(i);
  }
  cout << out << endl;
}


Compiler output:
a.cc: In function 'int main()':
a.cc:8:8: error: 'i' was not declared in this scope
    8 |   for (i = 0; i < s.size(); i+=2) {
      |        ^
Language: C++

#include <bits/stdc++.h>

int main() {
    cout << "ce" << endl;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:4:5: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
    4 |     cout << "ce" << endl;
      |     ^~~~
      |     std::cout
In file included from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:146,
                 from a.cc:1:
/usr/include/c++/14/iostream:63:18: note: 'std::cout' declared here
   63 |   extern ostream cout;          ///< Linked to standard output
      |                  ^~~~
a.cc:4:21: error: 'endl' was not declared in this scope; did you mean 'std::endl'?
    4 |     cout << "ce" << endl;
      |                     ^~~~
      |                     std::endl
In file included from /usr/include/c++/14/istream:41,
                 from /usr/include/c++/14/sstream:40,
                 from /usr/include/c++/14/complex:45,
                 from /usr/include/c++/14/ccomplex:39,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:127:
/usr/include/c++/14/ostream:744:5: note: 'std::endl' declared here
  744 |     endl(basic_ostream<_CharT, _Traits>& __os)
      |     ^~~~
Language: C++

#include<string>
#include<iostring>

int main(){
  std::string s;
  std::cin >> s;
  int n = s.size();
  for(int i = 0; i != n; i+=2)
    std::cout << s[i] ;
  std::cout << std::endl;
  return 0;
}

Compiler output:
a.cc:2:9: fatal error: iostring: No such file or directory
    2 | #include<iostring>
      |         ^~~~~~~~~~
compilation terminated.
Language: Java

import java.util.Scanner;

public class Main{
  public static void main(String[] args){
	Scanner sc = new Scanner(System.in);
    String s = sc.next();
    StringBuilder sb = new StringBuilder();
    for(int i = 0; i < s.length(); i = i + 2){
      char c = s.charAt(i);
      sb.add(c);
    } 
    System.out.println(sb);
  }
}




Compiler output:
Main.java:10: error: cannot find symbol
      sb.add(c);
        ^
  symbol:   method add(char)
  location: variable sb of type StringBuilder
1 error
Language: Java

import java.util.Scanner;
import java.util.List;
import java.util.ArrayList;
public class Main{
  public static void main(String[] args){
	Scanner sc = new Scanner(System.in);
    String s = sc.next();
    ArrayList<Char> list = new ArrayList<Char>();
    for(int i = 0; i < s.length; i = i + 2){
      char c = s.charAt(i);
      list.add(c);
    } 
    System.out.println(list);
  }
}




Compiler output:
Main.java:8: error: cannot find symbol
    ArrayList<Char> list = new ArrayList<Char>();
              ^
  symbol:   class Char
  location: class Main
Main.java:8: error: cannot find symbol
    ArrayList<Char> list = new ArrayList<Char>();
                                         ^
  symbol:   class Char
  location: class Main
Main.java:9: error: cannot find symbol
    for(int i = 0; i < s.length; i = i + 2){
                        ^
  symbol:   variable length
  location: variable s of type String
3 errors
Language: C++

#include<bits/stdc++.h>
using namespace std;
int main()
{
    string at;
    cin>>at;
    fot(int i=0;i<at.size();i+=2) cout<<at[i];
    cout<<endl;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:7:9: error: expected primary-expression before 'int'
    7 |     fot(int i=0;i<at.size();i+=2) cout<<at[i];
      |         ^~~
a.cc:7:17: error: 'i' was not declared in this scope
    7 |     fot(int i=0;i<at.size();i+=2) cout<<at[i];
      |                 ^
Language: C++

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef vector<long long> vll;
typedef vector<pair<int,int>> vpi;
typedef vector<pair<long long, long long>> vpl;
typedef pair<int,int> pii;
typedef pair<long long, long long> pll;
#define INF (int)(1e9)
#define MAXX 1.1529215e+18
#define inf 999999
#define EPS (1e-7)
#define rep(i,n) for(int i=0; i<(int)(n);i++)
#define REP(i,n) for(int i=1;i<=(int)(n);i++)
#define FOR(i,k,n) for(int i=(k);i<(int)(n);i++)
#define ALL(a)  a.begin(),a.end()
#define RALL(a) a.begin(),a.end(),greater<int>()
#define ROT(a) a.begin(),a.begin()+1,a.end()
#define RROT(a) a.begin(),a.end()-1,a.end()
#define PB push_back
#define MP make_pair
#define PI acos(-1.0)
#define sz(a) a.size()
const ll MOD = 1e9+7;
const int MAX = 10000000;
template<typename T1, typename T2> inline bool chmin(T1 &a, T2 b) { if (a > b) { a = b; return 1; } return 0; }
template<typename T1, typename T2> inline bool chmax(T1 &a, T2 b) { if (a < b) { a = b; return 1; } return 0; }
template<typename T> T gcd(T a, T b) { if (b == 0) return a; return gcd(b, a % b); }
//cout << 'H' << endl;
/*--------------------------------------------*/

int main(){
    //cout << fixed << setprecision(10)
    cin.tie(0);
    ios::sync_with_stdio(false);

    string s;
    cin >> s;

    rep(i,N){
        if(!i%2){
            cout << s[i];
        }
    }
}

Compiler output:
a.cc: In function 'int main()':
a.cc:40:11: error: 'N' was not declared in this scope
   40 |     rep(i,N){
      |           ^
a.cc:13:39: note: in definition of macro 'rep'
   13 | #define rep(i,n) for(int i=0; i<(int)(n);i++)
      |                                       ^
Language: C++

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef vector<long long> vll;
typedef vector<pair<int,int>> vpi;
typedef vector<pair<long long, long long>> vpl;
typedef pair<int,int> pii;
typedef pair<long long, long long> pll;
#define INF (int)(1e9)
#define MAXX 1.1529215e+18
#define inf 999999
#define EPS (1e-7)
#define rep(i,n) for(int i=0; i<(int)(n);i++)
#define REP(i,n) for(int i=1;i<=(int)(n);i++)
#define FOR(i,k,n) for(int i=(k);i<(int)(n);i++)
#define ALL(a)  a.begin(),a.end()
#define RALL(a) a.begin(),a.end(),greater<int>()
#define ROT(a) a.begin(),a.begin()+1,a.end()
#define RROT(a) a.begin(),a.end()-1,a.end()
#define PB push_back
#define MP make_pair
#define PI acos(-1.0)
#define sz(a) a.size()
const ll MOD = 1e9+7;
const int MAX = 10000000;
template<typename T1, typename T2> inline bool chmin(T1 &a, T2 b) { if (a > b) { a = b; return 1; } return 0; }
template<typename T1, typename T2> inline bool chmax(T1 &a, T2 b) { if (a < b) { a = b; return 1; } return 0; }
template<typename T> T gcd(T a, T b) { if (b == 0) return a; return gcd(b, a % b); }
//cout << 'H' << endl;
/*--------------------------------------------*/

int main(){
    //cout << fixed << setprecision(10)
    cin.tie(0);
    ios::sync_with_stdio(false);

    string s;
    cin >> s;

    rep(i,N){
        if(i %= 0){
            cout << s[i];
        }
    }
}

Compiler output:
a.cc: In function 'int main()':
a.cc:40:11: error: 'N' was not declared in this scope
   40 |     rep(i,N){
      |           ^
a.cc:13:39: note: in definition of macro 'rep'
   13 | #define rep(i,n) for(int i=0; i<(int)(n);i++)
      |                                       ^
a.cc:41:14: warning: division by zero [-Wdiv-by-zero]
   41 |         if(i %= 0){
      |            ~~^~~~
Language: C++

include <bits/stdc++.h>
using namespace std;
 
int main()
{

	string s;
	string answer;

	cin >> s;

	answer = s[0];

	for (int i = 1; i < s.size(); i++) { 
		
		if (i % 2 != 0 ) {
			answer = answer + s[i];
		}
	}

	cout << answer << endl;

	return 0;

}

Compiler output:
a.cc:1:1: error: 'include' does not name a type
    1 | include <bits/stdc++.h>
      | ^~~~~~~
a.cc: In function 'int main()':
a.cc:7:9: error: 'string' was not declared in this scope
    7 |         string s;
      |         ^~~~~~
a.cc:8:15: error: expected ';' before 'answer'
    8 |         string answer;
      |               ^~~~~~~
      |               ;
a.cc:10:9: error: 'cin' was not declared in this scope
   10 |         cin >> s;
      |         ^~~
a.cc:10:16: error: 's' was not declared in this scope
   10 |         cin >> s;
      |                ^
a.cc:12:9: error: 'answer' was not declared in this scope
   12 |         answer = s[0];
      |         ^~~~~~
a.cc:21:9: error: 'cout' was not declared in this scope
   21 |         cout << answer << endl;
      |         ^~~~
a.cc:21:27: error: 'endl' was not declared in this scope
   21 |         cout << answer << endl;
      |                           ^~~~
Language: Java

import java.util.*;
class Main
{
	public static void main(String[] args)
	{
		Scanner sc=new Scanner(System.in);
		String str=sc.nextLine(),
			   ansStr="";
		for(long i=0;i<str.length();i++)
		{
			if(i%2==0)
			{
				ansStr+=str.charAt(i);
			}	
		}
		System.out.println(ansStr);
	}
}

Compiler output:
Main.java:13: error: incompatible types: possible lossy conversion from long to int
				ansStr+=str.charAt(i);
				                   ^
Note: Some messages have been simplified; recompile with -Xdiags:verbose to get full output
1 error
Language: Java

import java.util.Scanner;

public class Oddstring {
	public static void main(String [] args){
		Scanner sc = new Scanner(System.in);
		String str = sc.next();
		for(int i=0 ; i<str.length(); i+=2){
			System.out.print(str.charAt(i));
		}
	}
}

Compiler output:
Main.java:3: error: class Oddstring is public, should be declared in a file named Oddstring.java
public class Oddstring {
       ^
1 error
Language: C++

#include <bits/stdc++.h>
using namespace std;
int main(){
  
  string s;
  cin >> s;
  
  for(int i=0; i<s.size(); i+=2;)
  cout << s;
  cout <<endl;
  
}

Compiler output:
a.cc: In function 'int main()':
a.cc:8:32: error: expected ')' before ';' token
    8 |   for(int i=0; i<s.size(); i+=2;)
      |      ~                         ^
      |                                )
a.cc:8:33: error: expected primary-expression before ')' token
    8 |   for(int i=0; i<s.size(); i+=2;)
      |                                 ^
Language: Java

import java.util.*;
public class Main{
 public static void main(String[] args){
   Scanner sc = new Scanner(System.in);
 
   String A = sc.next();
   int B = A.length();
 
   StringBuilder ans ="";
   for(int i= 0;i<B;i+=2)
   {
     ans.append(A.substring(i,i+1));
   }
 
   System.out.println(ans.toString());
 }
}

Compiler output:
Main.java:9: error: incompatible types: String cannot be converted to StringBuilder
   StringBuilder ans ="";
                      ^
1 error
Language: Java

import java.util.*;
public class Main{
 public static void main(String[] args){
   Scanner sc = new Scanner(System.in);
 
   String A = sc.next();
 
   StringBuilder ans ="";
   for(int i= 0;i<B;i+=2)
   {
     ans+= A.substring(i,i+1);
   }
 
   System.out.println(ans.toString());
 }
}

Compiler output:
Main.java:8: error: incompatible types: String cannot be converted to StringBuilder
   StringBuilder ans ="";
                      ^
Main.java:9: error: cannot find symbol
   for(int i= 0;i<B;i+=2)
                  ^
  symbol:   variable B
  location: class Main
Main.java:11: error: incompatible types: String cannot be converted to StringBuilder
     ans+= A.substring(i,i+1);
                      ^
3 errors
Language: Java

import java.util.*;
public class Main{
 public static void main(String[] args){
   Scanner sc = new Scanner(System.in);
 
   String A = sc.next();
   int B = A.length();
 
   String ans ="";
   for(int i= 0;i<B;i+=2)
   {
     ans+= A.substring(i,i+1); 
     if(i%1000==0) System.gc()
   }
 
   System.out.println(ans);
 }
}

Compiler output:
Main.java:13: error: ';' expected
     if(i%1000==0) System.gc()
                              ^
1 error
Language: C++

#include <iostream>
#include <string>
int main(){std::string s;std::cin>>s;for(int i=0;i!=s.size();++i)std::cout<<(i%2?"":s[i];}

Compiler output:
a.cc: In function 'int main()':
a.cc:3:81: error: operands to '?:' have different types 'const char*' and '__gnu_cxx::__alloc_traits<std::allocator<char>, char>::value_type' {aka 'char'}
    3 | int main(){std::string s;std::cin>>s;for(int i=0;i!=s.size();++i)std::cout<<(i%2?"":s[i];}
a.cc:3:89: error: expected ')' before ';' token
    3 | int main(){std::string s;std::cin>>s;for(int i=0;i!=s.size();++i)std::cout<<(i%2?"":s[i];}
      |                                                                             ~           ^
      |                                                                                         )
Language: C++

#include <iostream>
#include <string>
#include <boost/range/irange.hpp>

using namespace std;
using namespace boost;

int main(){
    string str;
    cin >> str;
    for(auto i : irange(0u, str.size(), 2)){
        cout << str[i];
    }
    cout << "\n";
}

Compiler output:
a.cc:3:10: fatal error: boost/range/irange.hpp: No such file or directory
    3 | #include <boost/range/irange.hpp>
      |          ^~~~~~~~~~~~~~~~~~~~~~~~
compilation terminated.
Language: C++

#include <bits/stdc++.h>
using namespace std;
string x;
long long ;
int main ()
{
    cin >> x;
    for (int i = 1; i <= x.length(); i += 2)
    	{
    		cout << x[i];
		}
    return 0;                       
}

Compiler output:
a.cc:4:6: error: declaration does not declare anything [-fpermissive]
    4 | long long ;
      |      ^~~~
Language: C++

<<string[2]<<string[4]<<string[6]<<string[8]<<string[10]<<string[12]

Compiler output:
a.cc:1:1: error: expected unqualified-id before '<<' token
    1 | <<string[2]<<string[4]<<string[6]<<string[8]<<string[10]<<string[12]
      | ^~
Language: C++

#include <iostream>

using namespace std;

int main()
{
    char c;
    int n1,n2;
    cin>>n1>>n2;
    char x;
    int y=0;
    int z=0;
    z=n1-n2;
    int i;
    for(i=97;i<97+n1;i++)
    {
        c=i;
        if(n1-n2==0)
        {
            cout<<c;
        }
        else
        {
            if(i==97)
            {
               cout<<c;
               x=c;
               y=n1-n2;
            }
            else
            {
                y=n1-n2;
                cout<<x;
                x=x;
                n1--;
            }
        }
    }
    temp1=i;
    for(i=i;i<z+temp1;i++)
    {
        c=i;
        cout<<c;
    }
    return 0;
}


Compiler output:
a.cc: In function 'int main()':
a.cc:39:5: error: 'temp1' was not declared in this scope
   39 |     temp1=i;
      |     ^~~~~
Language: C++

#include<bits/stdc++.h>
using namespace std;
int main(){
  string s;
  cin >> s;
  
  for(i = 1; i < s.size() + 1; i++){
    if(i % 2 != 0){
      cout << s[i-1];
    }
  }
  cout << endl;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:7:7: error: 'i' was not declared in this scope
    7 |   for(i = 1; i < s.size() + 1; i++){
      |       ^
Language: C++

#include <stdc++.h>
using namespace std;

int main(){
  string s;
  cin >> s;
  string answer="";
  for(int i=1;i<(s.size()-1)/2+1;i+=2){
    answer+=s.at(i);
  }
  cout << answer << endl;
}

Compiler output:
a.cc:1:10: fatal error: stdc++.h: No such file or directory
    1 | #include <stdc++.h>
      |          ^~~~~~~~~~
compilation terminated.
Language: C++

//#define _GLIBCXX_DEBUG
#include <bits/stdc++.h>
#include <numeric>
typedef long long Int;
#define rep(i,a,b) for(Int i=a;i<b;++i)
#define rrep(i,a,b) for(Int i=a;i>=b;--i)
using namespace std;

int main() {
    cin.tie(0); cout.tie(0);
    ios::sync_with_stdio(false);

    string s; cin >> s;
    for (int i = 0, i < s.size(); i += 2) cout << s[i];
}

Compiler output:
a.cc: In function 'int main()':
a.cc:14:22: error: expected ';' before '<' token
   14 |     for (int i = 0, i < s.size(); i += 2) cout << s[i];
      |                      ^~
      |                      ;
a.cc:14:23: error: expected primary-expression before '<' token
   14 |     for (int i = 0, i < s.size(); i += 2) cout << s[i];
      |                       ^
Language: C++

#include <string>
#include <map>
#include <stdio.h>
#include <cmath>
#include <vector>  

using namespace std;

string N;
int INDEX;
string HOGE;

int main() {
    cin >> N;
    int nLength = N.size();
    if (nLength < 1){
        return -1;
    }
    for(int i = 0; i < nLength; ++i){
        if(i % 2 == 0){
            HOGE += N[i];
        }
    }
    cout << HOGE << endl;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:14:5: error: 'cin' was not declared in this scope
   14 |     cin >> N;
      |     ^~~
a.cc:6:1: note: 'std::cin' is defined in header '<iostream>'; this is probably fixable by adding '#include <iostream>'
    5 | #include <vector>
  +++ |+#include <iostream>
    6 | 
a.cc:24:5: error: 'cout' was not declared in this scope
   24 |     cout << HOGE << endl;
      |     ^~~~
a.cc:24:5: note: 'std::cout' is defined in header '<iostream>'; this is probably fixable by adding '#include <iostream>'
a.cc:24:21: error: 'endl' was not declared in this scope
   24 |     cout << HOGE << endl;
      |                     ^~~~
a.cc:6:1: note: 'std::endl' is defined in header '<ostream>'; this is probably fixable by adding '#include <ostream>'
    5 | #include <vector>
  +++ |+#include <ostream>
    6 |
Language: C++

#include<bits/stdc++.h>
using namespace std;
int main(){
	char a[100000]; long long n = 1;
	while(cin >> a[n]){
		if(n % 2 == 1) cout << c;
		n++;
    } cout << endl;
	return 0;
}


Compiler output:
a.cc: In function 'int main()':
a.cc:6:40: error: 'c' was not declared in this scope
    6 |                 if(n % 2 == 1) cout << c;
      |                                        ^
Language: C++

#include<bits/stdc++.h>
using namespace std;
char a[100010];
int main()
{    
    gets(s);
    for(int i=0;i<strlen(a);i+=2)
    {
        printf("%c",a[i]);
    }
    cout<<endl;
    return 0;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:6:10: error: 's' was not declared in this scope
    6 |     gets(s);
      |          ^
a.cc:6:5: error: 'gets' was not declared in this scope; did you mean 'getw'?
    6 |     gets(s);
      |     ^~~~
      |     getw
Language: C++

#include <bits/stdc++.h>
using namespace std;

int main(){
  string s;
  cin >> s;
  for(int i=0;i<n;i++)if(i%2)cout << s.at(i);
  cout << endl;
}


Compiler output:
a.cc: In function 'int main()':
a.cc:7:17: error: 'n' was not declared in this scope
    7 |   for(int i=0;i<n;i++)if(i%2)cout << s.at(i);
      |                 ^
Language: C++

#include <bits/stdc++.h>
using namespace std;

int main() {
  string N
  cin >> N;
  cout << N.at(0);
  for(int i = 0; i < N.size()-3; i++){
      char a = N.at(i+2);
      cout << a;
  }
}

Compiler output:
a.cc: In function 'int main()':
a.cc:6:3: error: expected initializer before 'cin'
    6 |   cin >> N;
      |   ^~~
a.cc:7:11: error: 'N' was not declared in this scope
    7 |   cout << N.at(0);
      |           ^
Language: C++

#include <bits/stdc++.h>
using namespace std;

int main(){
    char a;
    string s;
    cin>>s;

    for(int i=0;i<10000;i++){
        if(i%2==0)cout<<string.at(i);
    }

    cout<<endl;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:10:31: error: expected primary-expression before '.' token
   10 |         if(i%2==0)cout<<string.at(i);
      |                               ^
Language: C++

#include <bits/stdc++.h>
using namespace std;

int main() {
  string s; cin >> s;
  for (int i = 0; i < N; i += 2) {
    cout << s.at(i);
  }
  cout << endl;
  
}


Compiler output:
a.cc: In function 'int main()':
a.cc:6:23: error: 'N' was not declared in this scope
    6 |   for (int i = 0; i < N; i += 2) {
      |                       ^
Language: C++

#include<bits/stdc++.h>
#include<algorithm>
#include<math.h>
#include<iostream>
using namespace std;
long long int lcm(long long int a,long long int b){
  long long int n;
  n=a*b/__gcd(a,b);
  return n;
}
using ll =long long int;
#define ci(a) cin>>a
#define co(a) cout<<a<<endl
#define gcd(a,b) __gcd(a,b)
#define vec vector<ll>
#define for(i,a,b) for(int i=a;i<b;i++)
#define sort(a,b) sort(a.begin(),b.end())
//gcd 最大公約数
//lcm 最小公倍数
//double 少数（変数）
//string 文字列（変数）
//sqrt 平方根
//ceil 天井関数
//floor 床関数
//abs 絶対値
//pow 累乗
//cbrt  立方根
//hypot 平方和の平方根
//(string-'0') 文字列を数字に変換
//vector<vector<int>> data(a,vector<b>(b)) a×b行列
//for(int i=0;i<a;i++)
//for(int j=0;j<b;j++)
//cin>>data.at(i).at(j)  a×b行列の入力
//floor(log10(a)+1) aの10進法での桁数

int main() {
  string a;
  ci(a);
  ll b=a.size();
  for(int i=0;i<b;i+=2)
    cout<<a[i];
  }

Compiler output:
a.cc:40:23: error: macro "for" requires 3 arguments, but only 1 given
   40 |   for(int i=0;i<b;i+=2)
      |                       ^
a.cc:16:9: note: macro "for" defined here
   16 | #define for(i,a,b) for(int i=a;i<b;i++)
      |         ^~~
a.cc: In function 'int main()':
a.cc:41:5: error: expected '(' before 'cout'
   41 |     cout<<a[i];
      |     ^~~~
      |     (
a.cc:41:13: error: 'i' was not declared in this scope
   41 |     cout<<a[i];
      |             ^
a.cc:42:3: error: expected primary-expression before '}' token
   42 |   }
      |   ^
a.cc:41:16: error: expected ';' before '}' token
   41 |     cout<<a[i];
      |                ^
      |                ;
   42 |   }
      |   ~             
a.cc:42:3: error: expected primary-expression before '}' token
   42 |   }
      |   ^
a.cc:41:16: error: expected ')' before '}' token
   41 |     cout<<a[i];
      |     ~~~~       ^
      |                )
   42 |   }
      |   ~             
a.cc:42:3: error: expected primary-expression before '}' token
   42 |   }
      |   ^
Language: C++

#include<iostream>
#include<string>
using namespace std;

int main(){
  string s;cin>>s;int N=s.size();string res = "";
  for(int i=0;i<N;i++){if(i%2==0)res.append(1, s[i])}
  cout<<res<<endl;
}


Compiler output:
a.cc: In function 'int main()':
a.cc:7:53: error: expected ';' before '}' token
    7 |   for(int i=0;i<N;i++){if(i%2==0)res.append(1, s[i])}
      |                                                     ^
      |                                                     ;
Language: C++

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;

int main() {
    string s;cin>>s;
    for (int i=0;i<s.size();i++)
        if (i%2==0)
            cout<<s[i]
    cout<<endl;
    return 0;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:9:23: error: expected ';' before 'cout'
    9 |             cout<<s[i]
      |                       ^
      |                       ;
   10 |     cout<<endl;
      |     ~~~~
Language: C++

#include <iostream>
#include <string>
using namespace std;

int main(){
  string S;
  cin>>S;
  string T;
  
  for(int i =0;i<S.size();i+=2){
    T+=S[i];
    }
  }
  cout<<T<<endl;
}
      
      

Compiler output:
a.cc:14:3: error: 'cout' does not name a type
   14 |   cout<<T<<endl;
      |   ^~~~
a.cc:15:1: error: expected declaration before '}' token
   15 | }
      | ^
Language: C++

#include <iostream>
using namespace std;

int main(){
  string S;
  cin>>S;
  string T;
  
  for(int i =0;i<S.size();i+=2){
    T+=S[i];
    }
  }
  cout<<T<<endl;
}
      
      

Compiler output:
a.cc:13:3: error: 'cout' does not name a type
   13 |   cout<<T<<endl;
      |   ^~~~
a.cc:14:1: error: expected declaration before '}' token
   14 | }
      | ^
Language: C++

#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)

int main() {
  string s;
  cin>>s;
  rep(i,N){
    if(i%2==0)cout << s[i];
  }
  return 0;  
    

}


Compiler output:
a.cc: In function 'int main()':
a.cc:8:9: error: 'N' was not declared in this scope
    8 |   rep(i,N){
      |         ^
a.cc:3:45: note: in definition of macro 'rep'
    3 | #define rep(i, n) for (int i = 0; i < (int)(n); i++)
      |                                             ^
Language: C++

#include<iostream>
#include<string>

using namespace std ;

int main(){
  int i ;
  string s,t='' ;
  
  cin >> s ;
  
  i=0 ;
  while(1){
    if(2*i>s.length()){break ;}
    t += s[2*i] ;
    i++ ;
  }
  
  cout << t <<endl;
}
    

Compiler output:
a.cc:8:14: error: empty character constant
    8 |   string s,t='' ;
      |              ^~
a.cc: In function 'int main()':
a.cc:8:14: error: conversion from 'char' to non-scalar type 'std::string' {aka 'std::__cxx11::basic_string<char>'} requested
Language: C++

#include<iostream>
#include<string>

using namespace std ;

int main(){
  int i ;
  string s,t ;
  
  cin >> s ;
  
  t='' ;
  i=0 ;
  while(1){
    if(2*i>s.length()){break ;}
    t += s[2*i] ;
    i++ ;
  }
  
  cout << t <<endl;
}
    

Compiler output:
a.cc:12:5: error: empty character constant
   12 |   t='' ;
      |     ^~
Language: C++

#include<iostream>
#include<string>

using namespace std ;

int main(){
  int i ;
  string s,t ;
  
  cin >> s ;
  
  t='' ;
  i=0 ;
  while(1){
    if(2*i>s.length()){break ;}
    t += s[2*i]) ;
    i++ ;
  }
  
  cout << t <<endl;
}
    

Compiler output:
a.cc:12:5: error: empty character constant
   12 |   t='' ;
      |     ^~
a.cc: In function 'int main()':
a.cc:16:16: error: expected ';' before ')' token
   16 |     t += s[2*i]) ;
      |                ^
      |                ;
Language: C++

#include<iostream>
#include<string>

using namespace std ;

int main(){
  int i ;
  string s,t ;
  
  cin >> s ;
  
  t='' ;
  i=0
  while(1){
    if(2*i+1>s.length()){break ;}
    t.append(s[2*i+1]) ;
    i++ ;
  }
  
  cout << t <<endl;
}
    

Compiler output:
a.cc:12:5: error: empty character constant
   12 |   t='' ;
      |     ^~
a.cc: In function 'int main()':
a.cc:13:6: error: expected ';' before 'while'
   13 |   i=0
      |      ^
      |      ;
   14 |   while(1){
      |   ~~~~~
Language: C++

#include <iostream>
#include <cstdlib>
#include <string>
#include <vector>
#include <stack>
#include <map>
#include <set>
#include <algorithm>
#include <numeric>
#include <math.h>
#include <stdio.h>
#include <ctype.h>
#include <ios> 
#include <iomanip>
using namespace std;

#define N_MAX   (100000)
#define LL_MAX_NUM (1LL<<60)
#define INF 1e7

typedef long long ll;
typedef long long int lli;

int main() {
	string s; cin >> s;
    int ssize = s.size();
    for (int i = 0; i < N; i++)
    {
        if (i % 2 == 0) cout << s[i];
    }
    cout << endl;
	return 0;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:27:25: error: 'N' was not declared in this scope
   27 |     for (int i = 0; i < N; i++)
      |                         ^
Language: C++

#include<iostream>
#include<cstring>
using namespace std;
int main(){
	char a[100001];
	gets(a);
	for(int i=0;i<strlen(a);i++){
		if(i%2==0){
			cout<<a[i];
		}
	}
	cout<<endl;
	return 0;
}


Compiler output:
a.cc: In function 'int main()':
a.cc:6:9: error: 'gets' was not declared in this scope; did you mean 'getw'?
    6 |         gets(a);
      |         ^~~~
      |         getw
Language: C++

int main()
{
    std::string s;
    std::cin >> s;
    for (int i = 0; i < s.size(); i += 2) { std::cout << s[i]; }
    std::cout << std::endl;
    return 0;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:3:10: error: 'string' is not a member of 'std'
    3 |     std::string s;
      |          ^~~~~~
a.cc:1:1: note: 'std::string' is defined in header '<string>'; this is probably fixable by adding '#include <string>'
  +++ |+#include <string>
    1 | int main()
a.cc:4:10: error: 'cin' is not a member of 'std'
    4 |     std::cin >> s;
      |          ^~~
a.cc:1:1: note: 'std::cin' is defined in header '<iostream>'; this is probably fixable by adding '#include <iostream>'
  +++ |+#include <iostream>
    1 | int main()
a.cc:4:17: error: 's' was not declared in this scope
    4 |     std::cin >> s;
      |                 ^
a.cc:5:50: error: 'cout' is not a member of 'std'
    5 |     for (int i = 0; i < s.size(); i += 2) { std::cout << s[i]; }
      |                                                  ^~~~
a.cc:5:50: note: 'std::cout' is defined in header '<iostream>'; this is probably fixable by adding '#include <iostream>'
a.cc:6:10: error: 'cout' is not a member of 'std'
    6 |     std::cout << std::endl;
      |          ^~~~
a.cc:6:10: note: 'std::cout' is defined in header '<iostream>'; this is probably fixable by adding '#include <iostream>'
a.cc:6:23: error: 'endl' is not a member of 'std'
    6 |     std::cout << std::endl;
      |                       ^~~~
a.cc:1:1: note: 'std::endl' is defined in header '<ostream>'; this is probably fixable by adding '#include <ostream>'
  +++ |+#include <ostream>
    1 | int main()
Language: C++

#include<bits/stdc++.h>
using namespace std;
int main()
{
  string s;
  cin >> s;
  for(int i=0; i<S.size(); i++){
    if(i%2!=0)
      cout << S.at(i);
  }
  cout << endl;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:7:18: error: 'S' was not declared in this scope
    7 |   for(int i=0; i<S.size(); i++){
      |                  ^
Language: C++

#include <iostream>
#include <string>
using namespace std;
 
int main() {
    string str;
    vector<string> ans;
    cin >> str;
    for(int i=0; i<str.length() ; i++){
      if((i+1)%2 != 0) cout << str[i] << flush;
    }
}



Compiler output:
a.cc: In function 'int main()':
a.cc:7:5: error: 'vector' was not declared in this scope
    7 |     vector<string> ans;
      |     ^~~~~~
a.cc:2:1: note: 'std::vector' is defined in header '<vector>'; this is probably fixable by adding '#include <vector>'
    1 | #include <iostream>
  +++ |+#include <vector>
    2 | #include <string>
a.cc:7:18: error: expected primary-expression before '>' token
    7 |     vector<string> ans;
      |                  ^
a.cc:7:20: error: 'ans' was not declared in this scope; did you mean 'abs'?
    7 |     vector<string> ans;
      |                    ^~~
      |                    abs
Language: Java

import java.util.Scanner;

public class ABC072B {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		char[] c = sc.nextLine().toCharArray();
		String ans = "";
		sc.close();
		for(int i = 0;i < c.length;i += 2) {
			ans += c[i];
		}
		System.out.println(ans);
	}
}

Compiler output:
Main.java:3: error: class ABC072B is public, should be declared in a file named ABC072B.java
public class ABC072B {
       ^
1 error
Language: Java

mport java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		char[] c = sc.nextLine().toCharArray();
		String ans = "";
		sc.close();
		for(int i = 0;i < c.length;i += 2) {
			ans += c[i];
		}
		System.out.println(ans);
	}
}

Compiler output:
Main.java:1: error: class, interface, enum, or record expected
mport java.util.Scanner;
^
1 error
Language: C++

mport java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		char[] c = sc.nextLine().toCharArray();
		String ans = "";
		sc.close();
		for(int i = 0;i < c.length;i += 2) {
			ans += c[i];
		}
		System.out.println(ans);
	}
}

Compiler output:
a.cc:1:1: error: 'mport' does not name a type
    1 | mport java.util.Scanner;
      | ^~~~~
a.cc:3:1: error: expected unqualified-id before 'public'
    3 | public class Main {
      | ^~~~~~
Language: C++

#include <bits/stdc++.h>
using namespace std;

string A;

int main(){
  cin >> A;
  int jisu = A.size();
  
  int res = 1;
  while(true){
    if(res > N+1) break;
  	cout << A[res - 1];
    res += 2;
  }
  cout << endl;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:12:14: error: 'N' was not declared in this scope
   12 |     if(res > N+1) break;
      |              ^
Language: Java

import java.util.*;

public class MAin{
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String s = sc.next();
        for(int i = 0; i < s.length();i=i+2){
            System.out.print(s.charAt(i));
        }
        System.out.println();
    }
}

Compiler output:
Main.java:3: error: class MAin is public, should be declared in a file named MAin.java
public class MAin{
       ^
1 error
Language: C++

#include <bits/stdc++>h>
using namespace std;
int main(){
  string s;
  cin >> s;
  for(int i=0;i<s.size();i++){
    if(i%2==0){
      cout << s[i];
    }
  }
  cout << endl;
}

Compiler output:
a.cc:1:24: warning: extra tokens at end of #include directive
    1 | #include <bits/stdc++>h>
      |                        ^
a.cc:1:10: fatal error: bits/stdc++>: No such file or directory
    1 | #include <bits/stdc++>h>
      |          ^~~~~~~~~~~~~~
compilation terminated.
Language: C++

#include <bits/stdc++.h>
using namespace std;
int main(){
  string s;
  cin >> s;
  N = s.size();
  for (int i=0; i<N; i++){
    if(i % 2 != 0){
      cout << s[i];
    }
  ]
}


Compiler output:
a.cc: In function 'int main()':
a.cc:6:3: error: 'N' was not declared in this scope
    6 |   N = s.size();
      |   ^
a.cc:11:3: error: expected primary-expression before ']' token
   11 |   ]
      |   ^
a.cc:12:2: error: expected '}' at end of input
   12 | }
      |  ^
a.cc:3:11: note: to match this '{'
    3 | int main(){
      |           ^
Language: C++

#include<bits/stdc++.h>
using namespace std;
int main()
{
    string s;
    cin>>s; 
    for (int j=0;j<s.length();j=j+2)
	{ 
    cout<<s[i]; 
    }
    cout<<endl; 
    return 0;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:9:13: error: 'i' was not declared in this scope
    9 |     cout<<s[i];
      |             ^
Language: C++

// luogu-judger-enable-o2
// luogu-judger-enable-o2
#include<bits/stdc++.h>
using namespace std;
char c;
int main (){
     while(cin>>c){
        i++;
        if(i%2==1) {
           cout<<c;
        }
    }
    cout<<endl;
	return 0;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:8:9: error: 'i' was not declared in this scope
    8 |         i++;
      |         ^
Language: C++

// luogu-judger-enable-o2
#include<bits/stdc++.h>
using namespace std;
char c[1000001];
int main (){
	for(long long i=1;i<=c.length();i++){
		cin>>c;
		if(i%2==1){
			cout<<c;
		}
    }
    cout<<endl;
	return 0;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:6:32: error: request for member 'length' in 'c', which is of non-class type 'char [1000001]'
    6 |         for(long long i=1;i<=c.length();i++){
      |                                ^~~~~~
Language: C++

// luogu-judger-enable-o2
#include<bits/stdc++.h>
using namespace std;
char c;
int main (){
	for(long long i=1;i<=c.length();i++){
		cin>>c;
		if(i%2==1){
			cout<<c;
		}
    }
    cout<<endl;
	return 0;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:6:32: error: request for member 'length' in 'c', which is of non-class type 'char'
    6 |         for(long long i=1;i<=c.length();i++){
      |                                ^~~~~~
Language: C++

// luogu-judger-enable-o2
#include<bits/stdc++.h>
using namespace std;
char c;
int main (){
	for(long long i=1;i<=s.length();i++){
		cin>>c;
		if(i%2==1){
			cout<<c;
		}
    }
    cout<<endl;
	return 0;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:6:30: error: 's' was not declared in this scope
    6 |         for(long long i=1;i<=s.length();i++){
      |                              ^
Language: C++

#include <bits/stdc++.h>
using namespace std;

int main() {
  string s;
  cin >> s;
  for (int i = 0; i < s.size(); i++){
    if (i%2 == 0)
      cout << s[i];
    end
    cout << endl;      
  }
}


Compiler output:
a.cc: In function 'int main()':
a.cc:10:8: error: expected ';' before 'cout'
   10 |     end
      |        ^
      |        ;
   11 |     cout << endl;
      |     ~~~~
a.cc:11:17: error: statement cannot resolve address of overloaded function
   11 |     cout << endl;
      |                 ^
Language: C++

#include <bits/stdc++.h>
using namespace std;

int main() {
  string s;
  cin >> s;
  for (int i = 0; i < s.size(); i++){
    if (i%2 == 0)
      cout << s[i];
    end;
    cout << endl;      
  }
}


Compiler output:
a.cc: In function 'int main()':
a.cc:10:8: error: statement cannot resolve address of overloaded function
   10 |     end;
      |        ^
Language: C++

#include <bits/stdc++.h>
using namespace std;

int main() {
  cin >> s;
  for (i = 0; i < s.size(); i++){
    if i%2 == 0
      cout << s[i];
    end
    cout << endl;      
  }
}


Compiler output:
a.cc: In function 'int main()':
a.cc:5:10: error: 's' was not declared in this scope
    5 |   cin >> s;
      |          ^
a.cc:6:8: error: 'i' was not declared in this scope
    6 |   for (i = 0; i < s.size(); i++){
      |        ^
a.cc:7:8: error: expected '(' before 'i'
    7 |     if i%2 == 0
      |        ^
      |        (
a.cc:9:8: error: expected ';' before 'cout'
    9 |     end
      |        ^
      |        ;
   10 |     cout << endl;
      |     ~~~~
a.cc:10:17: error: statement cannot resolve address of overloaded function
   10 |     cout << endl;
      |                 ^
Language: C++

#include<iostream>
using namespace sts;
 
int main(){
  string s;
  cin >> s;
  string ans;
  for(int i = 0; i < s.size();i++){
    if( (i&1) == 1){
      ans += s[i];
    }
  }
  cout << ans << endl;
}

Compiler output:
a.cc:2:17: error: 'sts' is not a namespace-name
    2 | using namespace sts;
      |                 ^~~
a.cc: In function 'int main()':
a.cc:5:3: error: 'string' was not declared in this scope
    5 |   string s;
      |   ^~~~~~
a.cc:5:3: note: suggested alternatives:
In file included from /usr/include/c++/14/iosfwd:41,
                 from /usr/include/c++/14/ios:40,
                 from /usr/include/c++/14/ostream:40,
                 from /usr/include/c++/14/iostream:41,
                 from a.cc:1:
/usr/include/c++/14/bits/stringfwd.h:77:33: note:   'std::string'
   77 |   typedef basic_string<char>    string;
      |                                 ^~~~~~
In file included from /usr/include/c++/14/bits/locale_classes.h:40,
                 from /usr/include/c++/14/bits/ios_base.h:41,
                 from /usr/include/c++/14/ios:44:
/usr/include/c++/14/string:76:11: note:   'std::pmr::string'
   76 |     using string    = basic_string<char>;
      |           ^~~~~~
a.cc:6:3: error: 'cin' was not declared in this scope; did you mean 'std::cin'?
    6 |   cin >> s;
      |   ^~~
      |   std::cin
/usr/include/c++/14/iostream:62:18: note: 'std::cin' declared here
   62 |   extern istream cin;           ///< Linked to standard input
      |                  ^~~
a.cc:6:10: error: 's' was not declared in this scope
    6 |   cin >> s;
      |          ^
a.cc:7:9: error: expected ';' before 'ans'
    7 |   string ans;
      |         ^~~~
      |         ;
a.cc:10:7: error: 'ans' was not declared in this scope; did you mean 'abs'?
   10 |       ans += s[i];
      |       ^~~
      |       abs
a.cc:13:3: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
   13 |   cout << ans << endl;
      |   ^~~~
      |   std::cout
/usr/include/c++/14/iostream:63:18: note: 'std::cout' declared here
   63 |   extern ostream cout;          ///< Linked to standard output
      |                  ^~~~
a.cc:13:11: error: 'ans' was not declared in this scope; did you mean 'abs'?
   13 |   cout << ans << endl;
      |           ^~~
      |           abs
a.cc:13:18: error: 'endl' was not declared in this scope; did you mean 'std::endl'?
   13 |   cout << ans << endl;
      |                  ^~~~
      |                  std::endl
/usr/include/c++/14/ostream:744:5: note: 'std::endl' declared here
  744 |     endl(basic_ostream<_CharT, _Traits>& __os)
      |     ^~~~
Language: C++

#include<iosteram>
using namespace sts;

int main(){
  string s;
  cin >> s;
  string ans;
  for(int i = 0; i < s.size();i++){
    if( (i&1) == 1){
      ans += s[i];
    }
  }
  cout << ans << endl;
}

Compiler output:
a.cc:1:9: fatal error: iosteram: No such file or directory
    1 | #include<iosteram>
      |         ^~~~~~~~~~
compilation terminated.
Language: C++

#include<stdio.h>
#include<string.h>
int main(void)
{
	char s[100000];
	scanf("%s",s);
	len=strlen(s);
	char a[len+1];
	for(i=0;i<=len-1;i++){
		if(i=0 || i%2==0){
			a[j]=s[i];
			j=j+1;
		}
	}
	printf("%s",a);
}

Compiler output:
a.cc: In function 'int main()':
a.cc:7:9: error: 'len' was not declared in this scope
    7 |         len=strlen(s);
      |         ^~~
a.cc:9:13: error: 'i' was not declared in this scope
    9 |         for(i=0;i<=len-1;i++){
      |             ^
a.cc:11:25: error: 'a' was not declared in this scope
   11 |                         a[j]=s[i];
      |                         ^
a.cc:11:27: error: 'j' was not declared in this scope
   11 |                         a[j]=s[i];
      |                           ^
a.cc:15:21: error: 'a' was not declared in this scope
   15 |         printf("%s",a);
      |                     ^
Language: C++

#include <bits/stdc++.h>
using namespace std;
int main(){
  string x;
  cin>>x;
  for(int i=0;i<x.strength(),i++;){
    if(i%2==1){
      cout<<x[i];
    }
  }
  cout<<endl;
  
}

Compiler output:
a.cc: In function 'int main()':
a.cc:6:19: error: 'std::string' {aka 'class std::__cxx11::basic_string<char>'} has no member named 'strength'; did you mean 'length'?
    6 |   for(int i=0;i<x.strength(),i++;){
      |                   ^~~~~~~~
      |                   length
Language: Java

mport java.util.Scanner;

/**
 *
 * @author C0117306
 */
public class Main {
     public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);
        String s = sc.next();
         for (int i = 0; i < s.length(); i++) {
             if (i%2==0) {
                 System.out.print(s.subSequence(i, i+1));
             }
         }
         System.out.println();
    }
}


Compiler output:
Main.java:1: error: class, interface, enum, or record expected
mport java.util.Scanner;
^
1 error
Language: C

#include <stdio.h>
#include <string.h>
int main(){
  char a[100001];
  scanf("%s",a);
  int n=strlen(s);
  for(int i=0;i<(n+1)/2;i++)printf("%c",2*i);
  return 0;
}

Compiler output:
main.c: In function 'main':
main.c:6:16: error: 's' undeclared (first use in this function)
    6 |   int n=strlen(s);
      |                ^
main.c:6:16: note: each undeclared identifier is reported only once for each function it appears in
Language: C++

#include<iostream>
#include<vector>
#include<algorithm>

using namespace std;

int main(){
    
    string s, v;

    cin >> s;

    for(int i=0;i<s.size();i++)
        if(i%2 == 0)
            v.push_back(s.substr(i,1));
    
    cout << v << endl;
    return 0;

}

Compiler output:
a.cc: In function 'int main()':
a.cc:15:33: error: cannot convert 'std::__cxx11::basic_string<char>' to 'char'
   15 |             v.push_back(s.substr(i,1));
      |                         ~~~~~~~~^~~~~
      |                                 |
      |                                 std::__cxx11::basic_string<char>
In file included from /usr/include/c++/14/string:54,
                 from /usr/include/c++/14/bits/locale_classes.h:40,
                 from /usr/include/c++/14/bits/ios_base.h:41,
                 from /usr/include/c++/14/ios:44,
                 from /usr/include/c++/14/ostream:40,
                 from /usr/include/c++/14/iostream:41,
                 from a.cc:1:
/usr/include/c++/14/bits/basic_string.h:1572:24: note:   initializing argument 1 of 'void std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::push_back(_CharT) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>]'
 1572 |       push_back(_CharT __c)
      |                 ~~~~~~~^~~
Language: C++

#include<iostream>
#include<vector>
#include<algorithm>

using namespace std;

int main(){
    
    string s;
    vector<string> v;

    cin >> s;

    for(int i=0;i<s.size();i++)
        if(i%2 == 0)
            v.push_back(s.substr(i,1))
    
    cout << v << endl;
    return 0;

}

Compiler output:
a.cc: In function 'int main()':
a.cc:16:39: error: expected ';' before 'cout'
   16 |             v.push_back(s.substr(i,1))
      |                                       ^
      |                                       ;
   17 | 
   18 |     cout << v << endl;
      |     ~~~~