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

#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for(int i=0;i<(int)(n);i++)
#define all(v) v.begin(),v.end()
#define rall(v) v.rbegin(),v.rend()
typedef long long ll;
#define _GLIBCXX_DEBUG
int main()	{
  string s;
  cin>>s;
  vector<bool>c(26,false);
  rep(i,n){
    c[s[i]-'a']=true;
  }
  rep(i,n){
    if(c[i]==false){
      cout<<(char)(i+'a')<<endl;
      return 0;
  }
    cout<<"None"<<endl;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:12:9: error: 'n' was not declared in this scope
   12 |   rep(i,n){
      |         ^
a.cc:3:38: note: in definition of macro 'rep'
    3 | #define rep(i,n) for(int i=0;i<(int)(n);i++)
      |                                      ^
a.cc:15:9: error: 'n' was not declared in this scope
   15 |   rep(i,n){
      |         ^
a.cc:3:38: note: in definition of macro 'rep'
    3 | #define rep(i,n) for(int i=0;i<(int)(n);i++)
      |                                      ^
a.cc:21:2: error: expected '}' at end of input
   21 | }
      |  ^
a.cc:8:17: note: to match this '{'
    8 | int main()      {
      |                 ^
Language: C++

#pragma GCC optimize("Ofast")
#include <bits/stdc++.h>
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define REP(i,a,b) for (int i = a; i < (b); ++i)
#define all(x) (x).begin(),(x).end()
#define rall(x) (x).rbegin(),(x).rend()
#define YY cout << "Yes" << endl;
#define NN cout << "No" << endl;
#define ve vector
#define pint pair<int,int>
const int INF = 1000000007;
const long double EPS = 1e-15;
const long double PI = acos(-1);
typedef long long ll;
using namespace std;
using Graph = vector<vector<int>>;
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }
ll gcd(ll a, ll b) { return b ? gcd(b, a%b) : a; }
ll lcm(ll a, ll b) { return (a * b) / gcd(a,b); }
// *max_element(all(d))
// priority_queue<int,vector<int>,greater<int>>
int solve(){
  string s;
  cin >> s;
  vector<int>cnt(26);
  rep(i,s.size)if(cnt[s[i] - 'a'] < 1)cnt[s[i] - 'a']++;
  rep(i,26){
    if(!cnt[i]){
      cout << 'a' + i << endl;
      return 0;
    }
  }
  cout << "None" << endl;
  return 0;
}
int main(){
  // ios::sync_with_stdio(false);cin.tie(nullptr);
  cout << fixed;cout << setprecision(16);
  solve();
  return 0;
}

Compiler output:
a.cc: In function 'int solve()':
a.cc:27:11: error: invalid use of member function 'std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::size_type std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::size() const [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>; size_type = long unsigned int]' (did you forget the '()' ?)
   27 |   rep(i,s.size)if(cnt[s[i] - 'a'] < 1)cnt[s[i] - 'a']++;
      |           ^
a.cc:3:39: note: in definition of macro 'rep'
    3 | #define rep(i,n) for (int i = 0; i < (n); ++i)
      |                                       ^
Language: C

#include<stdio.h>
#include<string.h>
int main(void){
  char alf[28]="abcdefghijklmnopqrstuvwxyz",str[100000];
  scanf("%s",str);
  for(int i=0;i<strlen(str);i++){
    for(int j=0;j<28;j++){
      if(alf[j]==str[i]){
        alf[j]='0';
      }
    }
  }
  for(i=0;i<28;i++){
    if(alf[i]!='0'){
      printf("%c",alf[i]);
      return 0;
    }
  }
  printf("None");
  return 0;
}

Compiler output:
main.c: In function 'main':
main.c:13:7: error: 'i' undeclared (first use in this function)
   13 |   for(i=0;i<28;i++){
      |       ^
main.c:13:7: note: each undeclared identifier is reported only once for each function it appears in
Language: C++

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

int main(){
  string S;
  cin >> S;
  string R = "None";
  map<char, int> map;
  for(int i = 0; i < N; i++){
    char c = S.at(i);
    if(!map.count(c)){
    	map[c] = 1;
    }
    else{
    	map.at(c)++;
    }
  }
  bool f = false;
  for(char i = 'a'; i <= 'z'; i++){
    if(!map.count(i)){
    	cout << i << endl;
      	f = true;
      	break;
    }
  }
  if(!f) cout << "None" << endl; 
}

Compiler output:
a.cc: In function 'int main()':
a.cc:9:22: error: 'N' was not declared in this scope
    9 |   for(int i = 0; i < N; i++){
      |                      ^
Language: C++

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

int main(){
  string s;
  cin >> s;
  bool app[26];
  for(int i = 0; i < 26: i++){
    app[i] = false;
  }
  for(int i = 0; i < 26; i++){
    app[s[i] - 'a'] = true;
  }
  for(int i = 0; i < 26; i++){
    if(!app[i]){
      cout << char (i + 'a') << endl;
      break;
    }
  }
  puts("None");
}

Compiler output:
a.cc: In function 'int main()':
a.cc:8:18: warning: range-based 'for' loops with initializer only available with '-std=c++20' or '-std=gnu++20' [-Wc++20-extensions]
    8 |   for(int i = 0; i < 26: i++){
      |                  ^
a.cc:8:24: error: expected ';' before ':' token
    8 |   for(int i = 0; i < 26: i++){
      |                        ^
      |                        ;
a.cc:11:3: error: expected primary-expression before 'for'
   11 |   for(int i = 0; i < 26; i++){
      |   ^~~
a.cc:10:4: error: expected ';' before 'for'
   10 |   }
      |    ^
      |    ;
   11 |   for(int i = 0; i < 26; i++){
      |   ~~~
a.cc:11:3: error: expected primary-expression before 'for'
   11 |   for(int i = 0; i < 26; i++){
      |   ^~~
a.cc:10:4: error: expected ')' before 'for'
   10 |   }
      |    ^
      |    )
   11 |   for(int i = 0; i < 26; i++){
      |   ~~~
a.cc:8:6: note: to match this '('
    8 |   for(int i = 0; i < 26: i++){
      |      ^
Language: C++

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

int main(){
	// sengen
	string s;
	// nyuryoku
	cin >> s;
	int length = s.size();
	// keisan
	vector<int> alpha.(26,0);
	for(int i=0;i<length;i++){
		alpha.at(s.at(i))++;
	}
	for(int i=0;i<27;i++){
		if(alpha.at(i) == 0){
			char c = alpha.at(i);
			cout << c;
			break;
		}
		if(i == 26){
			cout << "None" << endl;
			break;
		}
	}
}

Compiler output:
a.cc: In function 'int main()':
a.cc:11:26: error: expected initializer before '.' token
   11 |         vector<int> alpha.(26,0);
      |                          ^
a.cc:13:17: error: 'alpha' was not declared in this scope; did you mean 'isalpha'?
   13 |                 alpha.at(s.at(i))++;
      |                 ^~~~~
      |                 isalpha
a.cc:16:20: error: 'alpha' was not declared in this scope; did you mean 'isalpha'?
   16 |                 if(alpha.at(i) == 0){
      |                    ^~~~~
      |                    isalpha
Language: Java

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		//━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
		String s = sc.next();
		sc.close();
		Set<Character> list = new HashSet<>();
		for(int i = 0; i < s.length(); i++){
			list.add(s.charAt(i));
		  }
		for (char i='a';i<'z';i++) {
			if(!list.contains(i)) {
				System.out.println(i);
				return;
			}
		}
		System.out.println("None");
		
		//━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
	}
}

Compiler output:
Main.java:3: error: cannot find symbol
		Scanner sc = new Scanner(System.in);
		^
  symbol:   class Scanner
  location: class Main
Main.java:3: error: cannot find symbol
		Scanner sc = new Scanner(System.in);
		                 ^
  symbol:   class Scanner
  location: class Main
Main.java:7: error: cannot find symbol
		Set<Character> list = new HashSet<>();
		^
  symbol:   class Set
  location: class Main
Main.java:7: error: cannot find symbol
		Set<Character> list = new HashSet<>();
		                          ^
  symbol:   class HashSet
  location: class Main
4 errors
Language: C++

#include <iostream>
using namespace std;


int main() {
  string N;
  cin >> N;
  string ans = "abcdefghijklmnopqrstuvwxyz";

string res="0";
sort(ans.begin(), ans.end(), greater<int>());
for (int i=0; i<26;i++){
  if(N.find(ans[i])==std::string::npos){
    res=ans[i];
  }
}

if (res=="0"){
  res = "None";
}
  cout << res << endl;
}



Compiler output:
a.cc: In function 'int main()':
a.cc:11:1: error: 'sort' was not declared in this scope; did you mean 'short'?
   11 | sort(ans.begin(), ans.end(), greater<int>());
      | ^~~~
      | short
Language: C++

#include<iostream>
#include<string>
#include<cstdlib>
int main(){
  std::string s;
  std::cin >> s;
  int t,a[26],n = s.size();
  memset(a, 0, sizeof(a));
  for(int i = 0; i != n;  i++){
    t = s[i];
    a[t] += 1;
  }
  int i;
  char ch;
  for(i = 0; i < 26; i++){
    if(a[i] == 0){
      ch = i + 97;
      break;
    }
  }
	if(i == 26)
      std::cout << "None" << std::endl;
  	else
      std::cout << ch << std::endl;
  return 0;
}


Compiler output:
a.cc: In function 'int main()':
a.cc:8:3: error: 'memset' was not declared in this scope
    8 |   memset(a, 0, sizeof(a));
      |   ^~~~~~
a.cc:4:1: note: 'memset' is defined in header '<cstring>'; this is probably fixable by adding '#include <cstring>'
    3 | #include<cstdlib>
  +++ |+#include <cstring>
    4 | int main(){
Language: C++

#include<bits/stdc++.h>
using namespace std;
int main(){
  string a;
  cin >> a;
  int count  = 0;
  vector<int> key(26);
  for(int i=0;i<a.size();i++){
    key.at(a.at(i)-97)++;
  }
  for(int i = 0;i< 26;i++){
    if(key.at(i) != 0){
      cout << (char)(i+97) << endl;
      count = 1;#include<bits/stdc++.h>
using namespace std;
int main(){
  string a;
  cin >> a;
  int count  = 0;
  vector<int> key(26);
  for(int i=0;i<a.size();i++){
    cout << a.at(i)-97 << endl;
    key.at(a.at(i)-97)++;
  }
  for(int i = 0;i< 26;i++){
    if(key.at(i) == 0){
      cout << (char)(i+97) << endl;
      count = 1;
      break;
    }
  }
  if(count == 0)
    cout << "None" << endl;
}   

      break;
    }
  }
  if(count == 0)
    cout << "None" << endl;
}   

Compiler output:
a.cc:14:17: error: stray '#' in program
   14 |       count = 1;#include<bits/stdc++.h>
      |                 ^
a.cc: In function 'int main()':
a.cc:14:18: error: 'include' was not declared in this scope
   14 |       count = 1;#include<bits/stdc++.h>
      |                  ^~~~~~~
a.cc:14:26: error: 'bits' was not declared in this scope
   14 |       count = 1;#include<bits/stdc++.h>
      |                          ^~~~
a.cc:14:31: error: 'stdc' was not declared in this scope; did you mean 'std'?
   14 |       count = 1;#include<bits/stdc++.h>
      |                               ^~~~
      |                               std
a.cc:15:1: error: expected primary-expression before 'using'
   15 | using namespace std;
      | ^~~~~
a.cc:16:9: warning: empty parentheses were disambiguated as a function declaration [-Wvexing-parse]
   16 | int main(){
      |         ^~
a.cc:16:9: note: remove parentheses to default-initialize a variable
   16 | int main(){
      |         ^~
      |         --
a.cc:16:9: note: or replace parentheses with braces to value-initialize a variable
a.cc:16:11: error: a function-definition is not allowed here before '{' token
   16 | int main(){
      |           ^
Language: C++

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

    string s;
    vector<int> a(26);
    int count = 0;
    a[26] = {0};
    for(int i = 0; s[i] != "\n"; i++){
        a[s[i] - 'a'] += 1;
    }

    for(int i = 0; i < a.size(); i++){
        if(a[i] == 0){cout << i + 'a'; count = 1; break;}
    }

    if(count == 0) cout << "None";



    return 0;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:10:25: error: ISO C++ forbids comparison between pointer and integer [-fpermissive]
   10 |     for(int i = 0; s[i] != "\n"; i++){
Language: C++

#include <bits/stdc++.h>
using namespace std;
 
int main()
{
	int alphabetCount = 26;          // a to z = 26 
	string  S;
	string answer = "None";
	bool existFlag[alphabetCount-1];         
	
	cin >> S;

	for (int i = 0; i < alphabetCount; i++) {
		existFlag[i] = false;
	}
		
	for (int j = 0; j < S.size()  ; j++) {
		existFlag[S.at(j) - 'a'] = true;
	}
	
	for (int i = 0; i < alphabetCount; j++) {
		if (existFlag[i]) {
			answer = S.at(i);
			break;
		}	
	}
	
	cout << answer << endl;
	return 0;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:21:44: error: 'j' was not declared in this scope
   21 |         for (int i = 0; i < alphabetCount; j++) {
      |                                            ^
Language: C++

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

int main() {
  int a,c,p;
  char 1;
  string s;
  cin >> s;
  a = s.size();
  for (int i=0; i< 26;i++){
    c = 0;
    for (int j=0; j < p;j++){
      p = s[j] - 'a';
      if (p == i) c++;
    }
    if (c == 0){
      q = 'a' + i;
      cout << q << endl;
      return 0;
    }
  }
  cout << "None" << endl;
  return 0;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:7:8: error: expected unqualified-id before numeric constant
    7 |   char 1;
      |        ^
a.cc:18:7: error: 'q' was not declared in this scope
   18 |       q = 'a' + i;
      |       ^
Language: C++

int main(){
  string S;
  cin >> S;
  vector<bool> see(26);
  for(int i=0; i<S.size(); i++){
    see.at(S.at(i)-97)=true;
  }
  char ans;
  for(int i=0; i<26; i++) if(see.at(i)==false){
    ans=char(i+97);
    break;
  }
  if(ans) cout << ans << endl;
  else cout << "None" << endl;
}


Compiler output:
a.cc: In function 'int main()':
a.cc:2:3: error: 'string' was not declared in this scope
    2 |   string S;
      |   ^~~~~~
a.cc:3:3: error: 'cin' was not declared in this scope
    3 |   cin >> S;
      |   ^~~
a.cc:3:10: error: 'S' was not declared in this scope
    3 |   cin >> S;
      |          ^
a.cc:4:3: error: 'vector' was not declared in this scope
    4 |   vector<bool> see(26);
      |   ^~~~~~
a.cc:4:10: error: expected primary-expression before 'bool'
    4 |   vector<bool> see(26);
      |          ^~~~
a.cc:6:5: error: 'see' was not declared in this scope
    6 |     see.at(S.at(i)-97)=true;
      |     ^~~
a.cc:9:30: error: 'see' was not declared in this scope
    9 |   for(int i=0; i<26; i++) if(see.at(i)==false){
      |                              ^~~
a.cc:13:11: error: 'cout' was not declared in this scope
   13 |   if(ans) cout << ans << endl;
      |           ^~~~
a.cc:13:26: error: 'endl' was not declared in this scope
   13 |   if(ans) cout << ans << endl;
      |                          ^~~~
a.cc:14:8: error: 'cout' was not declared in this scope
   14 |   else cout << "None" << endl;
      |        ^~~~
a.cc:14:26: error: 'endl' was not declared in this scope
   14 |   else cout << "None" << endl;
      |                          ^~~~
Language: C

#include<stdio.h>
#include<string.h>
int main(){
  char s[10001];
  scanf("%s",s);
  int a=strlen(s),b[26]={0},c=-1;
  for(int i=0; i<a; i++){
    b[s[i]-'a']++
  }
  for(int i=0; i<26; i++){
    if(b[i]==0){c=i;break;}
  }
  if(c==-1){
    printf("None");
  }else{
    printf("%c",'a'+c);
  }
  return 0;}

Compiler output:
main.c: In function 'main':
main.c:8:18: error: expected ';' before '}' token
    8 |     b[s[i]-'a']++
      |                  ^
      |                  ;
    9 |   }
      |   ~
Language: C++

#include <bits/stdc++.h>
using namespace std;
#define int long long
#define rep(i,n) for(int i=0;i<n;i++)
#define rep1(i,n) for(int i=1;i<=n;i++)
#define rep2(i,n) for(int i=0;i<=n;i++)
#define repr(i,a,n) for(int i=a;i<n;i++)
#define all(a) a.begin(),a.end()
#define P pair<long long,long long>
#define double long double
#define INF 1e10
#define MOD 1e9+7
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }
using Graph = vector<vector<int>>;
signed main(){
  string a;
  cin>>a;
  for(char i='a';i<='z';i++){
  int c=0;
    rep(j,a.size()){
  if(a[j]==i)
    int c++;
  }
    if(c==0){
    cout<<i<<endl;
      return 0;
    }
  }
  cout<<"None"<<endl;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:23:10: error: expected initializer before '++' token
   23 |     int c++;
      |          ^~
Language: Java

import java.util.*;
public class Main{
 public static void main(String[] args){
   Scanner sc = new Scanner(System.in);
 
   char[] A = sc.next().toCharArray();   
   char[] alp = {'a','b','c','d','e','f','g','h','i',
                 'j','k','l','m','n','o','p','q','r',
                 's','t','u','v','w','x','y','z'};
   boolean flg = false;
 
   for(int i= 0;i<26;i++)
   {
     if(!A.contains(alp[i]))
     {
       System.out.println(alp[i]);
       break;
     }
   }
 
   if(flg) System.out.println("None");
 }
}

Compiler output:
Main.java:14: error: cannot find symbol
     if(!A.contains(alp[i]))
          ^
  symbol:   method contains(char)
  location: variable A of type char[]
1 error
Language: Java

import java.util.*;
public class Main{
 public static void main(String[] args){
   Scanner sc = new Scanner(System.in);
 
   char[] A = sc.next().toCharArray();   
   char[] alp = {'a','b','c','d','e','f','g','h','i',
                 'j','k','l','m','n','o','p','q','r',
                 's','t','u','v','w','x','y','z'};
   boolean flg = false;
 
   for(int i= 0;i<26;i+=+)
   {
     if(A.contains(alp[i]))
     {
       System.out.println(alp[i]);
       break;
     }
   }
 
   if(flg) System.out.println("None");
 }
}

Compiler output:
Main.java:12: error: illegal start of expression
   for(int i= 0;i<26;i+=+)
                         ^
1 error
Language: C++

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

int arr[26];
int main()
{
  string s;
  cin>>s;
  for(int i=0;i<26;i++) arr[i]=0;
  for(int i=0;i<s.length();i++)
  {
    arr[s[i]-'a']++;
  }
  int flag=0;
  for(int i=0;i<26;i++)
  {
    if(arr[i]=0)
    {
      flag=1;
      char a=char(i+'a');
      cout<<a<<endl;
      break;
    }
  }
  if(flag==1)break;
  else cout<<"None"<<endl;
  
}


Compiler output:
a.cc: In function 'int main()':
a.cc:25:14: error: break statement not within loop or switch
   25 |   if(flag==1)break;
      |              ^~~~~
Language: C++

#include<iostream>
#include<string>
#include<bitset>

int main() {
  std::string str;
  std::bitset<25> bit;
  std::cin >> str;
  for (int i=0; i<str.size(); i++) {
    bit.set(int(str.at(i)) - 'a', 1);
  }
  int flag = 0;
  char ans;
  for (int i=0; i<25; i++) {
    if (bit.at(i) == 0) {
      ans = 'a'+i;
      flag=1;
      break;
    }
  }
  if (flag) {
    std::cout << ans << std::endl;
  }
  else {
    std::cout << "None" << std::endl;
  }
}
  

Compiler output:
a.cc: In function 'int main()':
a.cc:15:13: error: 'class std::bitset<25>' has no member named 'at'
   15 |     if (bit.at(i) == 0) {
      |             ^~
Language: C++

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

int main(){
  string s;
  cin>>s;
  char c='a';
  for(int i=0;i<26;i++){
    if(s.find(c+i)==npos){
      cout<<c+i;
      return 0;
    }
  }
  cout<<"None";
}

Compiler output:
a.cc: In function 'int main()':
a.cc:9:21: error: 'npos' was not declared in this scope
    9 |     if(s.find(c+i)==npos){
      |                     ^~~~
Language: C++

#include <iostream>
#include <string>
#include <string.h>
#include <strings.h>
#include <bits/stdc++.h>
#include <bits/algorithmfwd.h>
#include <bits/mask_array.h>


#include <cmath>
#include <math.h>

using namespace std;
/*97-->122*/
int main()
{
    string s;
    cin>>s;
    int m=s.length();
    int c=m-1;
   int bgn[m];
   int ennd[m];
   int o=0;
        for(int j=122;j>96;j--){
             for(int i=0;i<m;i++){
                    if(s.at(i)==(char)j){
                        ennd[i]=j;

                    }
        }

    }
    int r=0;
    for(int x=97;x>123;x++){
             for(int y=0;y<m;y++){
                    if(s.at(y)==(char)x){
                        bgn[y]=x;

                    }
        }

    }
    o=0;
    r=0;
    sort(bgn,bgn+m);
    sort(ennd,ennd+c);
    int l;
    l=o;
    int u=r;
    int p=0;
    char ttt;
    for(int t=0;t<m;t++){
            p=0;
    for(;u<=l;u++){

                    if(s.at(t)==(char)u){
                        p++;
                    }
           if(p==c){
            ttt=s.at(t)
            break;
           }         
        }
     
                ttt=s.at(t);
            break;
        }  
    }
    cout<<ttt;
    return 0;
}


Compiler output:
a.cc: In function 'int main()':
a.cc:60:24: error: expected ';' before 'break'
   60 |             ttt=s.at(t)
      |                        ^
      |                        ;
   61 |             break;
      |             ~~~~~       
a.cc: At global scope:
a.cc:69:5: error: 'cout' does not name a type
   69 |     cout<<ttt;
      |     ^~~~
a.cc:70:5: error: expected unqualified-id before 'return'
   70 |     return 0;
      |     ^~~~~~
a.cc:71:1: error: expected declaration before '}' token
   71 | }
      | ^
Language: C++

#include <bits/stdc++.h>
#define ll long long
using namespace std;
const int N = 1e5+10;
char str[N];
int a[30];
int main() {
    cin >> str;
    for(int i = 0; str[i]; i ++) a[str[i]-'a']++;
    for(int i = 0; i < 26; i ++) {
        if(a[i] == 0) return 0*printf("%c\n",i+'a');
    }
   printf("None")
    return 0;
}


Compiler output:
a.cc: In function 'int main()':
a.cc:13:18: error: expected ';' before 'return'
   13 |    printf("None")
      |                  ^
      |                  ;
   14 |     return 0;
      |     ~~~~~~
Language: C++

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

int main() {
  string S;
  cin >> S;

  sort(S.begin(), S.end());
  S.erase(unique(S.begin(), S.end()), S.end());

  string ans = "None";

  for (int i = 1; i < S.size(); i++) {
    if (S.at(i) - S.at(i - 1) != 1) {
      ans = S.at(i - 1) + 0x01;
      break;
    }
  }

  if (S.size() == 25 && S.at(S.size() - 1) == 'y') ans = "z"

  cout << ((S.at(0) != 'a') ? "a" : ans) << endl;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:20:61: error: expected ';' before 'cout'
   20 |   if (S.size() == 25 && S.at(S.size() - 1) == 'y') ans = "z"
      |                                                             ^
      |                                                             ;
   21 | 
   22 |   cout << ((S.at(0) != 'a') ? "a" : ans) << endl;
      |   ~~~~
Language: C++

#include <bits/stdc++.h>
using namespace std;
#define REP(i, n) for(int i = 0; i < n; i++)
int main(){ 
    string s;
    cin s;
    for(char i='a';i<='z';i++){
        for(int j=0;j<s.size();j++){
            if(s[j]==i){
                break;
            }
            if(j==s.size()-1){
                cout<<i;
                return 0;
            }
        }
    }
    cout<<"None";
    return 0;
}


Compiler output:
a.cc: In function 'int main()':
a.cc:6:8: error: expected ';' before 's'
    6 |     cin s;
      |        ^~
      |        ;
Language: C++

#include<bits/stdc++.h>
using namespace std;
const int mod = 1000000007;
#define rep(i, n) for(int i = 0; i < (n); i++)

int int_len(int n) {
  int s=0;
  while(n!=0) s++, n/=10;
  return s;
}

int int_sum(int n) {
  int m=0,s=0,a=n;
  while(a!=0) s++, a/=10;
  for(int i=s-1;i>=0;i--) m+=n/((int)pow(10,i))-(n/((int)pow(10,i+1)))*10;
  return m;
}






int gcd(int a,int b)
{
 
  int r, tmp;
 
  
 
  /* 自然数 a > b を確認・入替 */
  if(a<b){
    tmp = a;
    a = b;
    b = tmp;
  }
 
  /* ユークリッドの互除法 */
  r = a % b;
  while(r!=0){
    a = b;
    b = r;
    r = a % b;
  }
 
 
 
  return b;
}







int fac(int n){
  int m=1;
  while(n>=1) m*=n,n--;
  return m;
}

int vec_sum(vector<int> v){
  int n=0;
  for(int i=0;i<v.size();i++) n+=v[i];
  return n;
}
///////////////////////////
int main() {
  string s;
  cin>>s;
  map<char,int> mp;
  rep(i,26){
    mp['a'+i]=0;
  }
  rep(i,s.size()){
    mp[s[i]]++;
  }
  for(auto c:mp){
    if(mp.second==0){
      cout<<mp.first<<endl;
      return 0;
    }
  }
  cout<<"None"<<endl;
  
}
///////////////////////////

Compiler output:
a.cc: In function 'int main()':
a.cc:80:11: error: 'class std::map<char, int>' has no member named 'second'
   80 |     if(mp.second==0){
      |           ^~~~~~
a.cc:81:16: error: 'class std::map<char, int>' has no member named 'first'
   81 |       cout<<mp.first<<endl;
      |                ^~~~~
Language: C++

#include<iostream>
#include<string>
using namespace std;
string s;
bool b[26];
int main(){
  cin>>s;
  for(int i=0;i<s.size();i++){
    b[s[i]-'a']=true;
  }
  for(int i=0;i<26;i++){
    if(!b[i]){
      cout<<char(i+'a');
      return 0;
    }
  }
  cout<<"None";
  return 0;
}
#include<iostream>
#include<string>
using namespace std;
string s;
bool b[26];
int main(){
  cin>>s;
  for(int i=0;i<s.size();i++){
    b[s[i]-'a']=true;
  }
  for(int i=0;i<26;i++){
    if(!b[i]){
      cout<<char(i+'a');
      return 0;
    }
  }
  cout<<"None";
  return 0;
}


Compiler output:
a.cc:23:8: error: redefinition of 'std::string s'
   23 | string s;
      |        ^
a.cc:4:8: note: 'std::string s' previously declared here
    4 | string s;
      |        ^
a.cc:24:6: error: redefinition of 'bool b [26]'
   24 | bool b[26];
      |      ^
a.cc:5:6: note: 'bool b [26]' previously declared here
    5 | bool b[26];
      |      ^
a.cc:25:5: error: redefinition of 'int main()'
   25 | int main(){
      |     ^~~~
a.cc:6:5: note: 'int main()' previously defined here
    6 | int main(){
      |     ^~~~
Language: C++

#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define rep2(i, s, n) for (int i = (s); i < (int)(n); i++)
typedef long long ll;

int main() {
    string S;
    cin >> S;
    string l = "abcdefghijklmnopqrstuvwxyz";
    bool flag2 = true;
    for (int i = 0; i < l.length(); i++){
        bool flag = true;
        for (int j = 0; j < S.length(); j++){
            if (S[j] == l[i]){
                flag == false;
                break;
            }
        }
        if (flag){
            cout << l[i] << endl;
            break;
        }
    }
    if (flag2)[
        cout << "None" << endl;
    ]
}


Compiler output:
a.cc: In function 'int main()':
a.cc:26:9: warning: capture of variable 'std::cout' with non-automatic storage duration
   26 |         cout << "None" << endl;
      |         ^~~~
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::ostream std::cout' declared here
   63 |   extern ostream cout;          ///< Linked to standard output
      |                  ^~~~
a.cc:26:13: error: expected ',' before '<<' token
   26 |         cout << "None" << endl;
      |             ^~~
      |             ,
a.cc:26:14: error: expected identifier before '<<' token
   26 |         cout << "None" << endl;
      |              ^~
a.cc:26:31: error: expected ']' before ';' token
   26 |         cout << "None" << endl;
      |                               ^
      |                               ]
a.cc: In lambda function:
a.cc:26:31: error: expected '{' before ';' token
a.cc: In function 'int main()':
a.cc:27:5: error: expected primary-expression before ']' token
   27 |     ]
      |     ^
Language: C++

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

    int n = S.length();
    vector<char> M(n);

    for (int i = 0; i < n; i++){
        M.at(i) = S[i];
    }

    sort(M.begin(), M.end());
    M.erase(unique(M.begin(), M.end()), M.end());
    int m = M.length();

    string L = "abcdefghijklmnopqrstuvwxyz";
    int count = 0;

    for (int i = 0; i < 26; i++){
        if(i <= m && M.at(i) != L[i]){
            cout << L[i] << endl;
            break;
        }
        else if (m < i){
            cout << L[i] << endl;
            break;
        }
        else {
            count++;
        }
    }

    if(count == 26) {
        cout << "None" << endl;
    }
}

Compiler output:
a.cc: In function 'int main()':
a.cc:17:15: error: 'class std::vector<char>' has no member named 'length'
   17 |     int m = M.length();
      |               ^~~~~~
Language: C++

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

    int n = S.length();
    vector<char> M(n);

    for (int i = 0; i < n; i++){
        M.at(i) = S[i];
    }

    sort(M.begin(), M.end());
    M.erase(unique(M.begin(), M.end()), M.end());
    int m = M.length();

    string L = "abcdefghijklmnopqrstuvwxyz";
    int count = 0;

    for (int i = 0; i < 26; i++){
        if(i <= m && M.at(i) != L[i]){
            cout << L[i] << endl;
            break;
        }
        else if (m > i){
            cout << L[i] << endl;
            break;
        }
        else {
            count++;
        }
    }

    if(count == 26) {
        cout << "None" << endl;
    }
}

Compiler output:
a.cc: In function 'int main()':
a.cc:17:15: error: 'class std::vector<char>' has no member named 'length'
   17 |     int m = M.length();
      |               ^~~~~~
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(char c = 'a';c <= z;c++){
      	if(s.indexOf(c)==-1){
        	System.out.println(c);
          return;
        }
      }
      System.out.println("None");
    }
}


Compiler output:
Main.java:6: error: cannot find symbol
      for(char c = 'a';c <= z;c++){
                            ^
  symbol:   variable z
  location: class Main
1 error
Language: C++

#include <bits/stdc++.h>
using namespace std;
 
int main() {
    string S;
    cin >> S;
    
 
    string ans = "None";
    for (char i = 'a'; i <= 'z'; i++){
 
        if(S.find(i) == string::npos){
            ans = i;
            break ;
        }
            
 
        
    }
 
    cout << ans << endl;
}
#include <bits/stdc++.h>
using namespace std;

int main() {
    string S;
    cin >> S;    
    string ans = "None";
    for (char i = 'a'; i <= 'z'; i++){

        if(S.find(i) == string::npos){
            ans = i;
            break ;
        }
                  
    }

    cout << ans << endl;
}


Compiler output:
a.cc:26:5: error: redefinition of 'int main()'
   26 | int main() {
      |     ^~~~
a.cc:4:5: note: 'int main()' previously defined here
    4 | int main() {
      |     ^~~~
Language: C++

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

int main(){
  string S[110000];
  for (int i=0;i<26;++i)cin>>S[i];
  
  bool app[26]={false};
  
  for (int i=0;i<26;++i){
    app[S[i]-'a']=true;
  }
  
  for (int i=0;i<26;++i){
    if (app[S[i]]==false){
      char ans =S[i];
      break;
    
  }
  if (ans)cout<<ans<<endl;
  else cout<<"None"<<endl;
}
    

Compiler output:
a.cc: In function 'int main()':
a.cc:12:13: error: no match for 'operator-' (operand types are 'std::string' {aka 'std::__cxx11::basic_string<char>'} and 'char')
   12 |     app[S[i]-'a']=true;
      |         ~~~~^~~~
      |            | |
      |            | char
      |            std::string {aka std::__cxx11::basic_string<char>}
In file included from /usr/include/c++/14/string:48,
                 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/stl_iterator.h:618:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr decltype ((__y.base() - __x.base())) std::operator-(const reverse_iterator<_Iterator>&, const reverse_iterator<_IteratorR>&)'
  618 |     operator-(const reverse_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:618:5: note:   template argument deduction/substitution failed:
a.cc:12:14: note:   'std::string' {aka 'std::__cxx11::basic_string<char>'} is not derived from 'const std::reverse_iterator<_Iterator>'
   12 |     app[S[i]-'a']=true;
      |              ^~~
/usr/include/c++/14/bits/stl_iterator.h:1790:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr decltype ((__x.base() - __y.base())) std::operator-(const move_iterator<_IteratorL>&, const move_iterator<_IteratorR>&)'
 1790 |     operator-(const move_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1790:5: note:   template argument deduction/substitution failed:
a.cc:12:14: note:   'std::string' {aka 'std::__cxx11::basic_string<char>'} is not derived from 'const std::move_iterator<_IteratorL>'
   12 |     app[S[i]-'a']=true;
      |              ^~~
a.cc:16:12: error: no match for 'operator[]' (operand types are 'bool [26]' and 'std::string' {aka 'std::__cxx11::basic_string<char>'})
   16 |     if (app[S[i]]==false){
      |            ^
a.cc:17:20: error: cannot convert 'std::string' {aka 'std::__cxx11::basic_string<char>'} to 'char' in initialization
   17 |       char ans =S[i];
      |                 ~~~^
      |                    |
      |                    std::string {aka std::__cxx11::basic_string<char>}
a.cc:21:7: error: 'ans' was not declared in this scope; did you mean 'abs'?
   21 |   if (ans)cout<<ans<<endl;
      |       ^~~
      |       abs
a.cc:23:2: error: expected '}' at end of input
   23 | }
      |  ^
a.cc:5:11: note: to match this '{'
    5 | int main(){
      |           ^
Language: C++

#include <iostream>
using namespace std;

int main(){
  string S[110000];
  for (int i=0;i<26;++i)cin>>S[i];
  
  bool app[26]={false};
  
  for (int i=0;i<26;++i){
    app[S[i]-'a']=true;
  }
  
  for (int i=0;i<26;++i){
    if (app[S[i]]==false){
      char ans =S[i];
      break;
    
  }
  if (ans)cout<<ans<<endl;
  else cout<<"None"<<endl;
}
    

Compiler output:
a.cc: In function 'int main()':
a.cc:11:13: error: no match for 'operator-' (operand types are 'std::string' {aka 'std::__cxx11::basic_string<char>'} and 'char')
   11 |     app[S[i]-'a']=true;
      |         ~~~~^~~~
      |            | |
      |            | char
      |            std::string {aka std::__cxx11::basic_string<char>}
In file included from /usr/include/c++/14/string:48,
                 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/stl_iterator.h:618:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr decltype ((__y.base() - __x.base())) std::operator-(const reverse_iterator<_Iterator>&, const reverse_iterator<_IteratorR>&)'
  618 |     operator-(const reverse_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:618:5: note:   template argument deduction/substitution failed:
a.cc:11:14: note:   'std::string' {aka 'std::__cxx11::basic_string<char>'} is not derived from 'const std::reverse_iterator<_Iterator>'
   11 |     app[S[i]-'a']=true;
      |              ^~~
/usr/include/c++/14/bits/stl_iterator.h:1790:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr decltype ((__x.base() - __y.base())) std::operator-(const move_iterator<_IteratorL>&, const move_iterator<_IteratorR>&)'
 1790 |     operator-(const move_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1790:5: note:   template argument deduction/substitution failed:
a.cc:11:14: note:   'std::string' {aka 'std::__cxx11::basic_string<char>'} is not derived from 'const std::move_iterator<_IteratorL>'
   11 |     app[S[i]-'a']=true;
      |              ^~~
a.cc:15:12: error: no match for 'operator[]' (operand types are 'bool [26]' and 'std::string' {aka 'std::__cxx11::basic_string<char>'})
   15 |     if (app[S[i]]==false){
      |            ^
a.cc:16:20: error: cannot convert 'std::string' {aka 'std::__cxx11::basic_string<char>'} to 'char' in initialization
   16 |       char ans =S[i];
      |                 ~~~^
      |                    |
      |                    std::string {aka std::__cxx11::basic_string<char>}
a.cc:20:7: error: 'ans' was not declared in this scope; did you mean 'abs'?
   20 |   if (ans)cout<<ans<<endl;
      |       ^~~
      |       abs
a.cc:22:2: error: expected '}' at end of input
   22 | }
      |  ^
a.cc:4:11: note: to match this '{'
    4 | int main(){
      |           ^
Language: C++

#include <iostream>
using namespace std;

int main(){
  string S[110000];
  for (int i=0;i<26;++i)cin>>S[i];
  
  int num[26]={0};
  for (int i=0;i<26;++i){
    num[S[i]]++;
  }
  
  for (int i=0;i<26;++i){
    if (num[S[i]]==0){
      char ans =S[i];
      break;
    }
  }
  if (ans)cout<<ans<<endl;
  else cout<<"None"<<endl;
}
    

Compiler output:
a.cc: In function 'int main()':
a.cc:10:8: error: no match for 'operator[]' (operand types are 'int [26]' and 'std::string' {aka 'std::__cxx11::basic_string<char>'})
   10 |     num[S[i]]++;
      |        ^
a.cc:14:12: error: no match for 'operator[]' (operand types are 'int [26]' and 'std::string' {aka 'std::__cxx11::basic_string<char>'})
   14 |     if (num[S[i]]==0){
      |            ^
a.cc:15:20: error: cannot convert 'std::string' {aka 'std::__cxx11::basic_string<char>'} to 'char' in initialization
   15 |       char ans =S[i];
      |                 ~~~^
      |                    |
      |                    std::string {aka std::__cxx11::basic_string<char>}
a.cc:19:7: error: 'ans' was not declared in this scope; did you mean 'abs'?
   19 |   if (ans)cout<<ans<<endl;
      |       ^~~
      |       abs
Language: C++

#include <iostream>
using namespace std;

int main(){
  string S[110000];
  for (int i=0;i<N;++i)cin>>S[i];
  
  int num[26]={0};
  for (int i=0;i<26;++i){
    num[S[i]]++;
  }
  
  for (int i=0;i<26;++i){
    if (num[S[i]]==0){
      char ans =S[i];
      break;
    }
  }
  if (ans)cout<<ans<<endl;
  else cout<<"None"<<endl;
}
    

Compiler output:
a.cc: In function 'int main()':
a.cc:6:18: error: 'N' was not declared in this scope
    6 |   for (int i=0;i<N;++i)cin>>S[i];
      |                  ^
a.cc:10:8: error: no match for 'operator[]' (operand types are 'int [26]' and 'std::string' {aka 'std::__cxx11::basic_string<char>'})
   10 |     num[S[i]]++;
      |        ^
a.cc:14:12: error: no match for 'operator[]' (operand types are 'int [26]' and 'std::string' {aka 'std::__cxx11::basic_string<char>'})
   14 |     if (num[S[i]]==0){
      |            ^
a.cc:15:20: error: cannot convert 'std::string' {aka 'std::__cxx11::basic_string<char>'} to 'char' in initialization
   15 |       char ans =S[i];
      |                 ~~~^
      |                    |
      |                    std::string {aka std::__cxx11::basic_string<char>}
a.cc:19:7: error: 'ans' was not declared in this scope; did you mean 'abs'?
   19 |   if (ans)cout<<ans<<endl;
      |       ^~~
      |       abs
Language: Java

import java.util.Scanner;

public class MainB071 {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);

		String S = sc.next();   ///標準入力
		int [] a = new int[26];
		for (char c: S.toCharArray()) {
			a[c-97] += 1;
		}
		String ans = "None";
		for (int i = 0; i < 26; i++) {
			if (a[i] == 0) {
				ans = Character.toString((char) (i+97));
				break;
			}
		}
	ans = "None";
		System.out.println( ans );
	}
}

Compiler output:
Main.java:3: error: class MainB071 is public, should be declared in a file named MainB071.java
public class MainB071 {
       ^
1 error
Language: C++

#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <set>
#include <cmath>
#include <utility>
#include <map>
#include <unordered_map>
using namespace std;
typedef long long int ll;

int main() {
  string S;
  cin>>S;
  
  vector<bool> b(26);
  for(int i=0;i<S.size();++i){
    b[S[i]-'a']
  }
  
}

Compiler output:
a.cc: In function 'int main()':
a.cc:19:16: error: expected ';' before '}' token
   19 |     b[S[i]-'a']
      |                ^
      |                ;
   20 |   }
      |   ~             
a.cc:19:15: warning: ignoring return value of 'std::vector<bool, _Alloc>::reference std::vector<bool, _Alloc>::operator[](size_type) [with _Alloc = std::allocator<bool>; reference = std::vector<bool>::reference; size_type = long unsigned int]', declared with attribute 'nodiscard' [-Wunused-result]
   19 |     b[S[i]-'a']
      |               ^
In file included from /usr/include/c++/14/vector:67,
                 from a.cc:3:
/usr/include/c++/14/bits/stl_bvector.h:1086:7: note: declared here
 1086 |       operator[](size_type __n)
      |       ^~~~~~~~
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;
	sort(S.begin(), S.end());
	char a = 'a';
	map<char, bool> Sexi;
	bool jdg = true;
	rep(i, S.size()){
		if(Sexi[S[i]].count)continue;
		else Sexi[S[i]] = true;
	}
	rep(i, 26){
		if(Sexi[a].count){
			continue;
			a++;
		}else{
			a++;
			cout << a << endl;
			jdg = false;
			break;
		}
	}
	if(jdg) cout << "None" << endl;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:13:31: error: request for member 'count' in 'Sexi.std::map<char, bool>::operator[]((*(const std::map<char, bool>::key_type*)(& S.std::__cxx11::basic_string<char>::operator[](((std::__cxx11::basic_string<char>::size_type)i)))))', which is of non-class type 'std::map<char, bool>::mapped_type' {aka 'bool'}
   13 |                 if(Sexi[S[i]].count)continue;
      |                               ^~~~~
a.cc:17:28: error: request for member 'count' in 'Sexi.std::map<char, bool>::operator[](a)', which is of non-class type 'std::map<char, bool>::mapped_type' {aka 'bool'}
   17 |                 if(Sexi[a].count){
      |                            ^~~~~
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;
	int N = S.size();
	sort(S.begin(), S.end());
	vector<pair<char, bool>> jdg(26);
	char invec = 'a';
	rep(i, 26){
		jdg[i].first = invec;
		jdg[i].second = true;
		invec++;
	}
	bool ch = true;
	rep(i, N){
		rep(j, 26){
			if(S[i] == jdg[j].first){
				jdg[j].second = false;
			}
		}
	}
	rep(i, 26){
		if(jdg[j].second){
			cout << jdg[i].first << endl;
			ch = false;
			break;
		}
	}
	if(ch) cout << "None" << endl;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:26:24: error: 'j' was not declared in this scope
   26 |                 if(jdg[j].second){
      |                        ^
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;
	int N = S.size();
	sort(S.begin(), S.end());
	vector<pair<char, bool>> jdg(26);
	char invec = a;
	rep(i, 26){
		jdg[i].first = invec;
		jdg[i].second = true;
		invec++;
	}
	bool ch = true;
	rep(i, N){
		rep(j, 26){
			if(S[i] == jdg[j].first){
				jdg[j].second = false;
			}
		}
	}
	rep(i, 26){
		if(jdg[j].second){
			cout << jdg[i].first << endl;
			ch = false;
			break;
		}
	}
	if(ch) cout << "None" << endl;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:11:22: error: 'a' was not declared in this scope
   11 |         char invec = a;
      |                      ^
a.cc:26:24: error: 'j' was not declared in this scope
   26 |                 if(jdg[j].second){
      |                        ^
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();
    int[] charCnt = new int[26];
  	
    for (char c: s.toCharArray()) {
      charCnt[c - 'a']++;
    }
    
    for (int i = 0; i < 26; i++) {
      if (charCnt[i] == 0) {
        System.out.println(("None"));
        System.exit(0);
      }
    }
    
    System.out.println((i + 'a'));
    System.exit(0);
  }
}

Compiler output:
Main.java:19: error: cannot find symbol
    System.out.println((i + 'a'));
                        ^
  symbol:   variable i
  location: class Main
1 error
Language: C++

#pragma GCC optimize "-O3"
#pragma GCC target ("avx")
#define _USE_MATH_DEFINES
#include<bits/stdc++.h>
#define int long long
#define rep(i,n) for(int i=0;i<n;++i)
#define vi vector<int>
#define vvi vector<vi>
#define pb push_back
#define pi pair<int,int>
#define vp vector<pair<int,int>>
#define mp make_pair
#define all(v) (v).begin(),(v).end()
#define fi first
#define se second
#define MEMSET(a) memset(a,0,sizeof(a))
#define inf (1ll<<60)
#define SORT(v) sort(all(v))
#define RSORT(v) sort(all(v),greater<int>())
#define SPEED ios::sync_with_stdio(false);cin.tie(0);cout<<fixed<<setprecision(12)
#define erase(i) erase(i, 1)
signed gcd(int a, int b){return b?gcd(b,a%b):a;}
signed lcm(int a, int b){return a*b/gcd(a,b);}
template<typename T> void remove(std::vector<T>& vector, unsigned int index){vector.erase(vector.begin() + index);}
//priority_queue<int, vi, greater<int> > que;//昇順

using namespace std;

const int mod=1e9+7;


signed main()
{
    string s;
    cin >> s;
    SORT(s);
    string ans = "";
    if(s[i] != 'a')
    {
        ans = "a";
        goto End;
    }
    rep(i,s.size()-1)
    {
        if(s[i+1] - s[i] > 1)
        {
            ans = s[i] + 1;
            break;
        }
    }
    if(ans == "" && s[s.size() - 1] != 'z')ans = s[s.size() - 1] + 1;
    if(ans == "")ans = "None"
    End:
    cout << ans << endl;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:38:10: error: 'i' was not declared in this scope
   38 |     if(s[i] != 'a')
      |          ^
a.cc:52:30: error: expected ';' before 'End'
   52 |     if(ans == "")ans = "None"
      |                              ^
      |                              ;
   53 |     End:
      |     ~~~                       
a.cc:41:14: error: label 'End' used but not defined
   41 |         goto End;
      |              ^~~
Language: C++

#include <bits/stdc++.h>

int main(){
    string s;
    std::cin>>s;
    int a=0x61;
    sort(s.begin(),s.end());
    for(int i=0;i<s.length();i++){if(s[i]==a)a++;else break;}
    std::cout<<char(a);
}

Compiler output:
a.cc: In function 'int main()':
a.cc:4:5: error: 'string' was not declared in this scope
    4 |     string s;
      |     ^~~~~~
a.cc:4:5: note: suggested alternatives:
In file included from /usr/include/c++/14/string:41,
                 from /usr/include/c++/14/bitset:52,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:52,
                 from a.cc:1:
/usr/include/c++/14/bits/stringfwd.h:77:33: note:   'std::string'
   77 |   typedef basic_string<char>    string;
      |                                 ^~~~~~
/usr/include/c++/14/string:76:11: note:   'std::pmr::string'
   76 |     using string    = basic_string<char>;
      |           ^~~~~~
a.cc:5:15: error: 's' was not declared in this scope
    5 |     std::cin>>s;
      |               ^
a.cc:7:5: error: 'sort' was not declared in this scope; did you mean 'std::sort'?
    7 |     sort(s.begin(),s.end());
      |     ^~~~
      |     std::sort
In file included from /usr/include/c++/14/algorithm:86,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:51:
/usr/include/c++/14/pstl/glue_algorithm_defs.h:296:1: note: 'std::sort' declared here
  296 | sort(_ExecutionPolicy&& __exec, _RandomAccessIterator __first, _RandomAccessIterator __last);
      | ^~~~