Language: C++

//int a = int(s); 文字列sをintへ
//小文字から大文字
//transform(a.begin(), a.end(), a.begin(), ::toupper);
//map 全探索
//auto begin = p.begin(), end = p.end();
//for (auto it = begin; it != end; it++) {}
//mapのキー：it->first mapのバリュー：it->second
//大文字判定 isupper(文字) 小文字判定 islower(文字)
//do{}while(next_permutation(ALL(配列)))
//小文字に対応する文字コード：S[i] - 'a'
//文字コード→小文字：(char)(数字+'a')
//グラフの距離:隣接行列で扱う
//bool型　初期値はTrue
//島渡りの問題：中間ノードに着目
//数が大きい時の比較はstring型で行う
//全て0になったか調べたい->0になるたびにcntする
//例外処理は最初にする
//x = p^m + q^n...の約数の個数:(n+1)*(m+1)....
//N!のどの素因数で何回割れるか
//⇔1~Nまでの数がそれぞれどの素因数で何回割り切れるかの和
//パズルの問題->一般化して全探索
//stack<ll> s;
//s.push(要素);s.top();s.pop();
//queue<ll> q;
//q.push(要素);q.front();q.pop();
//同じ作業繰り返す系の問題：収束先を見つける
//過半数：N/2.0で判定
//優先度付きキュー
//priority_queue<
//ll,
//vector<ll>
//> q;
#include <bits/stdc++.h>
#include <iostream>
#include <string>
#include <stdexcept>
#define rep(i,N) for(int i = 0; i < N;i++)
#define ALL(a) (a).begin(),(a).end()
#define ll long long int
#define PI 3.14159265358979323846264338327950L
using namespace std;

//割るやつ
const ll MOD = (pow(10, 9) + 7);

// K進数でのNの桁数
ll dig(ll N, ll K) {
	ll dig = 0;
	while (N) {
		dig++;
		N /= K;
	}
	return dig;
}
// a,bの最大公約数
ll gcd(ll a, ll b) {
	if (b == 0) return a;
	return gcd(b, a%b);
}

//a,bの最小公倍数
ll lcm(ll a, ll b) {
	ll g = gcd(a, b);
	return a / g * b;
}

//階乗計算
ll f(ll n) {
	if (n == 0 || n == 1) return 1;
	else return (n * f(n - 1));
}

//Nのd桁目の数
ll dignum(ll N, ll d) {
	ll x = pow(10, d);
	N %= x;
	ll y = pow(10, d - 1);
	N /= y;
	return N;
}

//Nをdで何回割れるか
ll divcnt(ll N, ll d) {
	ll ans = 0;
	while (1) {
		if (N%d == 0) {
			ans++;
			N /= d;
		}
		else break;
	}

	return ans;
}

//素数判定
bool prime(ll num) {
	if (num < 2) return false;
	else if (num == 2) return true;
	else if (num % 2 == 0) return false;
	double sqrtNum = sqrt(num);
	for (int i = 3; i <= sqrtNum; i += 2) {
		if (num % i == 0) return false;
	}
	return true;
}

//フィボナッチ数列
vector<ll> memo(pow(10, 6) + 1);
ll fibo(ll n) {
	if (n == 1) return 1;
	else if (n == 2) return 1;
	else if (memo[n] != 0) return memo[n];
	else return memo[n] = fibo(n - 1) + f(n - 2);
}

ll RS(ll N, ll P, ll M) {
	if (P == 0) return 1;
	if (P % 2 == 0) {
		ll t = RS(N, P / 2, M);
		return t * t % M;
	}
	return N * RS(N, P - 1, M);
}

vector<int> IntegerToVector(int bit, int N) {
    vector<int> S;
    for (int i = 0; i < N; ++i) {
        if (bit & (1 << i)) {
            S.push_back(i);
        }
    }
    return S;
}

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

	if(S == '0'){
		cout << "Yes" << endl;
		return 0;
	}
 
	ll sum = 0;
	rep(i, S.size()){
		sum += int(S[i]);
	}

	if(sum%9 == 0)cout << "Yes" << endl;
	else cout << "No" << endl;
}	

Compiler output:
a.cc: In function 'int main()':
a.cc:139:14: error: no match for 'operator==' (operand types are 'std::string' {aka 'std::__cxx11::basic_string<char>'} and 'char')
  139 |         if(S == '0'){
      |            ~ ^~ ~~~
      |            |    |
      |            |    char
      |            std::string {aka std::__cxx11::basic_string<char>}
In file included from /usr/include/c++/14/regex:68,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:181,
                 from a.cc:33:
/usr/include/c++/14/bits/regex.h:1103:5: note: candidate: 'template<class _BiIter> bool std::__cxx11::operator==(const sub_match<_BiIter>&, const sub_match<_BiIter>&)'
 1103 |     operator==(const sub_match<_BiIter>& __lhs, const sub_match<_BiIter>& __rhs)
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1103:5: note:   template argument deduction/substitution failed:
a.cc:139:17: note:   'std::string' {aka 'std::__cxx11::basic_string<char>'} is not derived from 'const std::__cxx11::sub_match<_BiIter>'
  139 |         if(S == '0'){
      |                 ^~~
/usr/include/c++/14/bits/regex.h:1199:5: note: candidate: 'template<class _Bi_iter, class _Ch_traits, class _Ch_alloc> bool std::__cxx11::operator==(__sub_match_string<_Bi_iter, _Ch_traits, _Ch_alloc>&, const sub_match<_BiIter>&)'
 1199 |     operator==(const __sub_match_string<_Bi_iter, _Ch_traits, _Ch_alloc>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1199:5: note:   template argument deduction/substitution failed:
a.cc:139:17: note:   mismatched types 'const std::__cxx11::sub_match<_BiIter>' and 'char'
  139 |         if(S == '0'){
      |                 ^~~
/usr/include/c++/14/bits/regex.h:1274:5: note: candidate: 'template<class _Bi_iter, class _Ch_traits, class _Ch_alloc> bool std::__cxx11::operator==(const sub_match<_BiIter>&, __sub_match_string<_Bi_iter, _Ch_traits, _Ch_alloc>&)'
 1274 |     operator==(const sub_match<_Bi_iter>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1274:5: note:   template argument deduction/substitution failed:
a.cc:139:17: note:   'std::string' {aka 'std::__cxx11::basic_string<char>'} is not derived from 'const std::__cxx11::sub_match<_BiIter>'
  139 |         if(S == '0'){
      |                 ^~~
/usr/include/c++/14/bits/regex.h:1366:5: note: candidate: 'template<class _Bi_iter> bool std::__cxx11::operator==(const typename std::iterator_traits<_Iter>::value_type*, const sub_match<_BiIter>&)'
 1366 |     operator==(typename iterator_traits<_Bi_iter>::value_type const* __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1366:5: note:   template argument deduction/substitution failed:
a.cc:139:17: note:   mismatched types 'const std::__cxx11::sub_match<_BiIter>' and 'char'
  139 |         if(S == '0'){
      |                 ^~~
/usr/include/c++/14/bits/regex.h:1441:5: note: candidate: 'template<class _Bi_iter> bool std::__cxx11::operator==(const sub_match<_BiIter>&, const typename std::iterator_traits<_Iter>::value_type*)'
 1441 |     operator==(const sub_match<_Bi_iter>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1441:5: note:   template argument deduction/substitution failed:
a.cc:139:17: note:   'std::string' {aka 'std::__cxx11::basic_string<char>'} is not derived from 'const std::__cxx11::sub_match<_BiIter>'
  139 |         if(S == '0'){
      |                 ^~~
/usr/include/c++/14/bits/regex.h:1534:5: note: candidate: 'template<class _Bi_iter> bool std::__cxx11::operator==(const typename std::iterator_traits<_Iter>::value_type&, const sub_match<_BiIter>&)'
 1534 |     operator==(typename iterator_traits<_Bi_iter>::value_type const& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1534:5: note:   template argument deduction/substitution failed:
a.cc:139:17: note:   mismatched types 'const std::__cxx11::sub_match<_BiIter>' and 'char'
  139 |         if(S == '0'){
      |                 ^~~
/usr/include/c++/14/bits/regex.h:1613:5: note: candidate: 'template<class _Bi_iter> bool std::__cxx11::operator==(const sub_match<_BiIter>&, const typename std::iterator_traits<_Iter>::value_type&)'
 1613 |     operator==(const sub_match<_Bi_iter>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1613:5: note:   template argument deduction/substitution failed:
a.cc:139:17: note:   'std::string' {aka 'std::__cxx11::basic_string<char>'} is not derived from 'const std::__cxx11::sub_match<_BiIter>'
  139 |         if(S == '0'){
      |                 ^~~
/usr/include/c++/14/bits/regex.h:2186:5: note: candidate: 'template<class _Bi_iter, class _Alloc> bool std::__cxx11::operator==(const match_results<_BiIter, _Alloc>&, const match_results<_BiIter, _Alloc>&)'
 2186 |     operator==(const match_results<_Bi_iter, _Alloc>& __m1,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:2186:5: note:   template argument deduction/substitution failed:
a.cc:139:17: note:   'std::string' {aka 'std::__cxx11::basic_string<char>'} is not derived from 'const std::__cxx11::match_results<_BiIter, _Alloc>'
  139 |         if(S == '0'){
      |                 ^~~
In file included from /usr/include/c++/14/bits/stl_algobase.h:64,
                 from /usr/include/c++/14/algorithm:60,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:51:
/usr/include/c++/14/bits/stl_pair.h:1033:5: note: candidate: 'template<class _T1, class _T2> constexpr bool std::operator==(const pair<_T1, _T2>&, const pair<_T1, _T2>&)'
 1033 |     operator==(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_pair.h:1033:5: note:   template argument deduction/substitution failed:
a.cc:139:17: note:   'std::string' {aka 'std::__cxx11::basic_string<char>'} is not derived from 'const std::pair<_T1, _T2>'
  139 |         if(S == '0'){
      |                 ^~~
In file included from /usr/include/c++/14/bits/stl_algobase.h:67:
/usr/include/c++/14/bits/stl_iterator.h:441:5: note: candidate: 'template<class _Iterator> constexpr bool std::operator==(const reverse_iterator<_Iterator>&, const reverse_iterator<_Iterator>&)'
  441 |     operator==(const reverse_iterator<_Iterator>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:441:5: note:   template argument deduction/substitution failed:
a.cc:139:17: note:   'std::string' {aka 'std::__cxx11::basic_string<char>'} is not derived from 'const std::reverse_iterator<_Iterator>'
  139 |         if(S == '0'){
      |                 ^~~
/usr/include/c++/14/bits/stl_iterator.h:486:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr bool std::operator==(const reverse_iterator<_Iterator>&, const reverse_iterator<_IteratorR>&)'
  486 |     operator==(const reverse_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:486:5: note:   template argument deduction/substitution failed:
a.cc:139:17: note:   'std::string' {aka 'std::__cxx11::basic_string<char>'} is not derived from 'const std::reverse_iterator<_Iterator>'
  139 |         if(S == '0'){
      |                 ^~~
/usr/include/c++/14/bits/stl_iterator.h:1667:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr bool std::operator==(const move_iterator<_IteratorL>&, const move_iterator<_IteratorR>&)'
 1667 |     operator==(const move_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1667:5: note:   template argument deduction/substitution failed:
a.cc:139:17: note:   'std::string' {aka 'std::__cxx11::basic_string<char>'} is not derived from 'const std::move_iterator<_IteratorL>'
  139 |         if(S == '0'){
      |                 ^~~
/usr/include/c++/14/bits/stl_iterator.h:1737:5: note: candidate: 'template<class _Iterator> constexpr bool std::operator==(const move_iterator<_IteratorL>&, const move_iterator<_IteratorL>&)'
 1737 |     operator==(const move_iterator<_Iterator>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1737:5: note:   template argument deduction/substitution failed:
a.cc:139:17: note:   'std::string' {aka 'std::__cxx11::basic_string<char>'} is not derived from 'const std::move_iterator<_IteratorL>'
  139 |         if(S == '0'){
      |                 ^~~
In file included from /usr/include/c++/14/bits/char_traits.h:42,
                 from /usr/include/c++/14/string:42,
                 from /usr/include/c++/14/bitset:52,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:52:
/usr/include/c++/14/bits/postypes.h:192:5: note: candidate: 'template<class _StateT> bool std::operator==(const fpos<_StateT>&, const fpos<_StateT>&)'
  192 |     operator==(const fpos<_StateT>& __lhs, const fpos<_StateT>& __rhs)
      |     ^~~~~~~~
/usr/include/c++/14/bits/postypes.h:192:5: note:   template argument deduction/substitution failed:
a.cc:139:17: note:   'std::string' {aka 'std::__cxx11::basic_string<char>'} is not derived from 'const std::fpos<_StateT>'
  139 |         if(S == '0'){
      |                 ^~~
In file included from /usr/include/c++/14/string:43:
/usr/include/c++/14/bits/allocator.h:235:5: note: candidate: 'template<class _T1, class _T2> bool std::operator==(const allocator<_CharT>&, const allocator<_T2>&)'
  235 |     operator==(const allocator<_T1>&, const allocator<_T2>&)
      |     ^~~~~~~~
/usr/include/c++/14/bits/allocator.h:235:5: note:   template argument deduction/substitution failed:
a.cc:139:17: note:   'std::string' {aka 'std::__cxx11::basic_string<char>'} is not derived from 'const std::allocator<_CharT>'
  139 |         if(S == '0'){
      |                 ^~~
In file included from /usr/include/c++/14/bits/basic_string.h:47,
                 from /usr/include/c++/14/string:54:
/usr/include/c++/14/string_view:629:5: note: candidate: 'template<class _CharT, class _Traits> constexpr bool std::operator==(basic_string_view<_CharT, _Traits>, __type_identity_t<basic_string_view<_CharT, _Traits> >)'
  629 |     operator==(basic_string_view<_CharT, _Traits> __x,
      |     ^~~~~~~~
/usr/include/c++/14/string_view:629:5: note:   template argument deduction/substitution failed:
a.cc:139:17: note:   'std::__cxx11::basic_string<char>' is not derived from 'std::bas