Language: C++

 #include <iostream>
#include <cstdio>
#include <algorithm>
#include <cmath>
#include <vector>
#include <list>
#include <set>
#include <map>
#include <queue>
#include <stack>
#include <cctype>
#include <cassert>
#include <climits>
#include <string>
#include <bitset>
#include <cfloat>
 #include <iostream>
#include <cstdio>
#include <algorithm>
#include <cmath>
#include <vector>
#include <list>
#include <set>
#include <map>
#include <queue>
#include <stack>
#include <cctype>
#include <cassert>
#include <climits>
#include <string>
#include <bitset>
#include <cfloat>
#include <unordered_set>
#include <iomanip>
using namespace std;
typedef long double ld;
typedef long long int ll;
typedef unsigned long long int ull;
typedef pair<int,int> pii;
typedef vector<int> vi;
typedef vector<char> vc;
typedef vector<bool> vb;
typedef vector<double> vd;
typedef vector<string> vs;
typedef vector<ll> vll;
typedef vector<pair<int,int> > vpii;
typedef vector<vector<int> > vvi;
typedef vector<vector<char> > vvc;
typedef vector<vector<string> > vvs;
typedef vector<vector<ll> > vvll;
#define rep(i,n) for(int i = 0; i < (n); ++i)
#define rrep(i,n) for(int i = 1; i <= (n); ++i)
#define irep(it, stl) for(auto it = stl.begin(); it != stl.end(); it++)
#define drep(i,n) for(int i = (n) - 1; i >= 0; --i)
#define fin(ans) cout << (ans) << endl
#define mp(p,q) make_pair(p, q)
#define pb(n) push_back(n)
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define Sort(a) sort(a.begin(), a.end())
#define Rort(a) sort(a.rbegin(), a.rend())
#define MATHPI acos(-1)
int dx8[8] = {1, 0, -1, 0, 1, -1, -1, 1};
int dy8[8] = {0, 1, 0, -1, 1, 1, -1, -1};
int dx4[4] = {1, 0, -1, 0};
int dy4[4] = {0, 1, 0, -1};
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;}
template<typename A, size_t N, typename T> void Fill(A (&array)[N], const T &val){ fill((T*)array, (T*)(array+N), val); }
struct io{io(){ios::sync_with_stdio(false);cin.tie(0);}};
const int INF = INT_MAX;
const ll LLINF = 1LL<<60;
const ll MOD = 1000000007;
const double EPS = 1e-9;

//問題文が複雑な時は具体例を出して、小さい方から考えていく
//形だけが同じなら良くて、a~前の文字列で使った一番大きい文字+1が次の文字列で使える
//あとは形が同じでその中の辞書順最強をdfsで作っていく

int Q;
string s;
string rev;

int main(){
      cin >> s;
      rev = s;//最初はrevも同じ
      reverse(rev.begin(),rev.end());
      cin >> Q;

      rep(i,Q){
          int x;
          cin >> x;
          if(x == 1){
              //swap
              s.swap(rev);
          }else{
              //revには逆の操作を行う
              int y;
              string c;
              cin >> y >> c;
              if(y == 1){
                  //普通のには前に、revには後ろに,insertはO(N)なのだが、先頭をしてすれば早いのでokっぽい
                  s.push_back(c);
                  rev.insert(0,c);//insertとの第二引数はstringなので注意
              }else{
                  rev.push_back(c);
                  s.insert(0,c);
              }
          }
      }

      fin(s);
      
}

Compiler output:
a.cc: In function 'int main()':
a.cc:103:31: error: cannot convert 'std::string' {aka 'std::__cxx11::basic_string<char>'} to 'char'
  103 |                   s.push_back(c);
      |                               ^
      |                               |
      |                               std::string {aka 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)
      |                 ~~~~~~~^~~
a.cc:106:33: error: cannot convert 'std::string' {aka 'std::__cxx11::basic_string<char>'} to 'char'
  106 |                   rev.push_back(c);
      |                                 ^
      |                                 |
      |                                 std::string {aka std::__cxx11::basic_string<char>}
/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)
      |                 ~~~~~~~^~~