Language: C++

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

///assic value of ('0'-'9') is(48 - 57) and (a-z) is (97-122) and (A-Z) is(65-90) and 32 for space
typedef long long int ll;
typedef pair<ll, ll> pii;
typedef vector<pii> vii;
#define  pb push_back
// #define f(i,a,b) for(ll i=a;i<b;i++)
#define f(i,a,b,c) for(ll i=a;i<b;i+=c)
#define fo(i,a,b) for(ll i = a; i<=b;i++)
#define rf(i,a,b)  for(ll i=a;i>=b;i--)
#define vll vector<ll>
#define tests() int test_cases ; cin >> test_cases ; while(test_cases--)
#define ub upper_bound
#define lb lower_bound
#define all(v) v.begin(),v.end()
#define MAXN 100010
#define MOD 1000000007
#define deb(x) cout << '>' << #x << ':' << x << endl;
#define sp " "
#define MS(x,y) memset(x,y,sizeof(x))
#define INF 1000000000000000000

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

    //tests(){}
    //v/ll fis;
    //cout<<fis.size();
    ll n;
    cin>>n;
    bool ans = true;
    std::vector<char> a(n);
    std::map<string , ll> m;
    for (int i = 0; i < n; ++i)
    {
    	cin>>a[i];
    	m[a[i]]++;
    }
    for(auto x:m){
    	cout<<x.first<<endl;
    }
    return 0;
}




Compiler output:
a.cc: In function 'int main()':
a.cc:41:10: error: no match for 'operator[]' (operand types are 'std::map<std::__cxx11::basic_string<char>, long long int>' and '__gnu_cxx::__alloc_traits<std::allocator<char>, char>::value_type' {aka 'char'})
   41 |         m[a[i]]++;
      |          ^
In file included from /usr/include/c++/14/map:63,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:152,
                 from a.cc:1:
/usr/include/c++/14/bits/stl_map.h:504:7: note: candidate: 'std::map<_Key, _Tp, _Compare, _Alloc>::mapped_type& std::map<_Key, _Tp, _Compare, _Alloc>::operator[](const key_type&) [with _Key = std::__cxx11::basic_string<char>; _Tp = long long int; _Compare = std::less<std::__cxx11::basic_string<char> >; _Alloc = std::allocator<std::pair<const std::__cxx11::basic_string<char>, long long int> >; mapped_type = long long int; key_type = std::__cxx11::basic_string<char>]'
  504 |       operator[](const key_type& __k)
      |       ^~~~~~~~
/usr/include/c++/14/bits/stl_map.h:504:34: note:   no known conversion for argument 1 from '__gnu_cxx::__alloc_traits<std::allocator<char>, char>::value_type' {aka 'char'} to 'const std::map<std::__cxx11::basic_string<char>, long long int>::key_type&' {aka 'const std::__cxx11::basic_string<char>&'}
  504 |       operator[](const key_type& __k)
      |                  ~~~~~~~~~~~~~~~~^~~
/usr/include/c++/14/bits/stl_map.h:524:7: note: candidate: 'std::map<_Key, _Tp, _Compare, _Alloc>::mapped_type& std::map<_Key, _Tp, _Compare, _Alloc>::operator[](key_type&&) [with _Key = std::__cxx11::basic_string<char>; _Tp = long long int; _Compare = std::less<std::__cxx11::basic_string<char> >; _Alloc = std::allocator<std::pair<const std::__cxx11::basic_string<char>, long long int> >; mapped_type = long long int; key_type = std::__cxx11::basic_string<char>]'
  524 |       operator[](key_type&& __k)
      |       ^~~~~~~~
/usr/include/c++/14/bits/stl_map.h:524:29: note:   no known conversion for argument 1 from '__gnu_cxx::__alloc_traits<std::allocator<char>, char>::value_type' {aka 'char'} to 'std::map<std::__cxx11::basic_string<char>, long long int>::key_type&&' {aka 'std::__cxx11::basic_string<char>&&'}
  524 |       operator[](key_type&& __k)
      |                  ~~~~~~~~~~~^~~