Language: C++

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

int main(){
    int s; cin >> s;
    vector<int> a;
    int n = 1;
    int c = s;

    a.push_back(s);

    while (1){
        n++;
        if (c % 2 == 0){
            c = c / 2;
        } else {
            c = 3 * c + 1;
        }

        if (n != 2){
            int result = find(a.begin(), a.end(), c);
            if (result != a.end()){
                a.push_back(c);
                break;
            }
        }
        
        a.push_back(c);
    }

    cout << n << endl;
    return 0;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:23:30: error: cannot convert '__gnu_cxx::__normal_iterator<int*, std::vector<int> >' to 'int' in initialization
   23 |             int result = find(a.begin(), a.end(), c);
      |                          ~~~~^~~~~~~~~~~~~~~~~~~~~~~
      |                              |
      |                              __gnu_cxx::__normal_iterator<int*, std::vector<int> >
a.cc:24:24: error: no match for 'operator!=' (operand types are 'int' and 'std::vector<int>::iterator')
   24 |             if (result != a.end()){
      |                 ~~~~~~ ^~ ~~~~~~~
      |                 |              |
      |                 int            std::vector<int>::iterator
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:1:
/usr/include/c++/14/bits/regex.h:1132:5: note: candidate: 'template<class _BiIter> bool std::__cxx11::operator!=(const sub_match<_BiIter>&, const sub_match<_BiIter>&)'
 1132 |     operator!=(const sub_match<_BiIter>& __lhs, const sub_match<_BiIter>& __rhs)
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1132:5: note:   template argument deduction/substitution failed:
a.cc:24:33: note:   mismatched types 'const std::__cxx11::sub_match<_BiIter>' and 'int'
   24 |             if (result != a.end()){
      |                                 ^
/usr/include/c++/14/bits/regex.h:1212:5: 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>&)'
 1212 |     operator!=(const __sub_match_string<_Bi_iter, _Ch_traits, _Ch_alloc>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1212:5: note:   template argument deduction/substitution failed:
a.cc:24:33: note:   mismatched types 'std::__cxx11::__sub_match_string<_Bi_iter, _Ch_traits, _Ch_alloc>' and 'int'
   24 |             if (result != a.end()){
      |                                 ^
/usr/include/c++/14/bits/regex.h:1305:5: 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>&)'
 1305 |     operator!=(const sub_match<_Bi_iter>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1305:5: note:   template argument deduction/substitution failed:
a.cc:24:33: note:   mismatched types 'const std::__cxx11::sub_match<_BiIter>' and 'int'
   24 |             if (result != a.end()){
      |                                 ^
/usr/include/c++/14/bits/regex.h:1379:5: note: candidate: 'template<class _Bi_iter> bool std::__cxx11::operator!=(const typename std::iterator_traits<_Iter>::value_type*, const sub_match<_BiIter>&)'
 1379 |     operator!=(typename iterator_traits<_Bi_iter>::value_type const* __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1379:5: note:   template argument deduction/substitution failed:
a.cc:24:33: note:   'std::vector<int>::iterator' is not derived from 'const std::__cxx11::sub_match<_BiIter>'
   24 |             if (result != a.end()){
      |                                 ^
/usr/include/c++/14/bits/regex.h:1473:5: note: candidate: 'template<class _Bi_iter> bool std::__cxx11::operator!=(const sub_match<_BiIter>&, const typename std::iterator_traits<_Iter>::value_type*)'
 1473 |     operator!=(const sub_match<_Bi_iter>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1473:5: note:   template argument deduction/substitution failed:
a.cc:24:33: note:   mismatched types 'const std::__cxx11::sub_match<_BiIter>' and 'int'
   24 |             if (result != a.end()){
      |                                 ^
/usr/include/c++/14/bits/regex.h:1547:5: note: candidate: 'template<class _Bi_iter> bool std::__cxx11::operator!=(const typename std::iterator_traits<_Iter>::value_type&, const sub_match<_BiIter>&)'
 1547 |     operator!=(typename iterator_traits<_Bi_iter>::value_type const& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1547:5: note:   template argument deduction/substitution failed:
a.cc:24:33: note:   'std::vector<int>::iterator' is not derived from 'const std::__cxx11::sub_match<_BiIter>'
   24 |             if (result != a.end()){
      |                                 ^
/usr/include/c++/14/bits/regex.h:1647:5: note: candidate: 'template<class _Bi_iter> bool std::__cxx11::operator!=(const sub_match<_BiIter>&, const typename std::iterator_traits<_Iter>::value_type&)'
 1647 |     operator!=(const sub_match<_Bi_iter>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1647:5: note:   template argument deduction/substitution failed:
a.cc:24:33: note:   mismatched types 'const std::__cxx11::sub_match<_BiIter>' and 'int'
   24 |             if (result != a.end()){
      |                                 ^
/usr/include/c++/14/bits/regex.h:2213:5: note: candidate: 'template<class _Bi_iter, class _Alloc> bool std::__cxx11::operator!=(const match_results<_BiIter, _Alloc>&, const match_results<_BiIter, _Alloc>&)'
 2213 |     operator!=(const match_results<_Bi_iter, _Alloc>& __m1,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:2213:5: note:   template argument deduction/substitution failed:
a.cc:24:33: note:   mismatched types 'const std::__cxx11::match_results<_BiIter, _Alloc>' and 'int'
   24 |             if (result != a.end()){
      |                                 ^
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:1052:5: note: candidate: 'template<class _T1, class _T2> constexpr bool std::operator!=(const pair<_T1, _T2>&, const pair<_T1, _T2>&)'
 1052 |     operator!=(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_pair.h:1052:5: note:   template argument deduction/substitution failed:
a.cc:24:33: note:   mismatched types 'const std::pair<_T1, _T2>' and 'int'
   24 |             if (result != a.end()){
      |                                 ^
In file included from /usr/include/c++/14/bits/stl_algobase.h:67:
/usr/include/c++/14/bits/stl_iterator.h:455:5: note: candidate: 'template<class _Iterator> constexpr bool std::operator!=(const reverse_iterator<_Iterator>&, const reverse_iterator<_Iterator>&)'
  455 |     operator!=(const reverse_iterator<_Iterator>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:455:5: note:   template argument deduction/substitution failed:
a.cc:24:33: note:   mismatched types 'const std::reverse_iterator<_Iterator>' and 'int'
   24 |             if (result != a.end()){
      |                                 ^
/usr/include/c++/14/bits/stl_iterator.h:500:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr bool std::operator!=(const reverse_iterator<_Iterator>&, const reverse_iterator<_IteratorR>&)'
  500 |     operator!=(const reverse_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:500:5: note:   template argument deduction/substitution failed:
a.cc:24:33: note:   mismatched types 'const std::reverse_iterator<_Iterator>' and 'int'
   24 |             if (result != a.end()){
      |                                 ^
/usr/include/c++/14/bits/stl_iterator.h:1686:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr bool std::operator!=(const move_iterator<_IteratorL>&, const move_iterator<_IteratorR>&)'
 1686 |     operator!=(const move_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1686:5: note:   template argument deduction/substitution failed:
a.cc:24:33: note:   mismatched types 'const std::move_iterator<_IteratorL>' and 'int'
   24 |             if (result != a.end()){
      |                                 ^
/usr/include/c++/14/bits/stl_iterator.h:1753:5: note: candidate: 'template<class _Iterator> constexpr bool std::operator!=(const move_iterator<_IteratorL>&, const move_iterator<_IteratorL>&)'
 1753 |     operator!=(const move_iterator<_Iterator>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1753:5: note:   template argument deduction/substitution failed:
a.cc:24:33: note:   mismatched types 'const std::move_iterator<_IteratorL>' and 'int'
   24 |             if (result != a.end()){
      |                                 ^
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:197:5: note: candidate: 'template<class _StateT> bool std::operator!=(const fpos<_StateT>&, const fpos<_StateT>&)'
  197 |     operator!=(const fpos<_StateT>& __lhs, const fpos<_StateT>& __rhs)
      |     ^~~~~~~~
/usr/include/c++/14/bits/postypes.h:197:5: note:   template argument deduction/substitution failed:
a.cc:24:33: note:   mismatched types 'const std::fpos<_StateT>' and 'int'
   24 |             if (result != a.end()){
      |                                 ^
In file included from /usr/include/c++/14/string:43:
/usr/include/c++/14/bits/allocator.h:243:5: note: candidate: 'template<class _T1, class _T2> bool std::operator!=(const allocator<_CharT>&, const allocator<_T2>&)'
  243 |     operator!=(const allocator<_T1>&, const allocator<_T2>&)
      |     ^~~~~~~~
/usr/include/c++/14/bits/allocator.h:243:5: note:   template argument deduction/substitution failed:
a.cc:24:33: note:   mismatched types 'const std::allocator<_CharT>' and 'int'
   24 |             if (result != a.end()){
      |                                 ^
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:651:5: note: candidate: 'template<class _CharT, class _Traits> constexpr bool std::operator!=(basic_string_view<_CharT, _Traits>, basic_string_view<_CharT, _Traits>)'
  651 |     operator!=(basic_string_v