Language: C++

#include <iostream>
#include <set>
using namespace std;
 
int main(){
  int count = 0;
  set<long> st;
  long tmp = 0;
  cin >> tmp;
  while(cin >> tmp){
   	 st.insert(tmp);
  }
  
  auto a_itr = st.begin();
  while(a_itr != st.end()){
  	auto b_itr = a_itr + 1;
    while(b_itr != st.end()){
      	auto c_itr = b_itr + 1;
      	while(c_itr != st.end()){
          	long a = *a_itr, b = *b_itr, c = *c_itr;
          	if(a + b > c && b + c > a && c + a > b){
              	++count;
            }
          c_itr++;
        }
      	b_itr++;
    }
    a_itr++;
  }
  
  cout << count << endl;
  
  return 0;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:16:28: error: no match for 'operator+' (operand types are 'std::_Rb_tree_const_iterator<long int>' and 'int')
   16 |         auto b_itr = a_itr + 1;
      |                      ~~~~~ ^ ~
      |                      |       |
      |                      |       int
      |                      std::_Rb_tree_const_iterator<long int>
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:627:5: note: candidate: 'template<class _Iterator> constexpr std::reverse_iterator<_Iterator> std::operator+(typename reverse_iterator<_Iterator>::difference_type, const reverse_iterator<_Iterator>&)'
  627 |     operator+(typename reverse_iterator<_Iterator>::difference_type __n,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:627:5: note:   template argument deduction/substitution failed:
a.cc:16:30: note:   mismatched types 'const std::reverse_iterator<_Iterator>' and 'int'
   16 |         auto b_itr = a_itr + 1;
      |                              ^
/usr/include/c++/14/bits/stl_iterator.h:1798:5: note: candidate: 'template<class _Iterator> constexpr std::move_iterator<_IteratorL> std::operator+(typename move_iterator<_IteratorL>::difference_type, const move_iterator<_IteratorL>&)'
 1798 |     operator+(typename move_iterator<_Iterator>::difference_type __n,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1798:5: note:   template argument deduction/substitution failed:
a.cc:16:30: note:   mismatched types 'const std::move_iterator<_IteratorL>' and 'int'
   16 |         auto b_itr = a_itr + 1;
      |                              ^
In file included from /usr/include/c++/14/string:54:
/usr/include/c++/14/bits/basic_string.h:3598:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> std::__cxx11::basic_string<_CharT, _Traits, _Allocator> std::operator+(const __cxx11::basic_string<_CharT, _Traits, _Allocator>&, const __cxx11::basic_string<_CharT, _Traits, _Allocator>&)'
 3598 |     operator+(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3598:5: note:   template argument deduction/substitution failed:
a.cc:16:30: note:   'std::_Rb_tree_const_iterator<long int>' is not derived from 'const std::__cxx11::basic_string<_CharT, _Traits, _Allocator>'
   16 |         auto b_itr = a_itr + 1;
      |                              ^
/usr/include/c++/14/bits/basic_string.h:3616:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> std::__cxx11::basic_string<_CharT, _Traits, _Allocator> std::operator+(const _CharT*, const __cxx11::basic_string<_CharT, _Traits, _Allocator>&)'
 3616 |     operator+(const _CharT* __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3616:5: note:   template argument deduction/substitution failed:
a.cc:16:30: note:   mismatched types 'const _CharT*' and 'std::_Rb_tree_const_iterator<long int>'
   16 |         auto b_itr = a_itr + 1;
      |                              ^
/usr/include/c++/14/bits/basic_string.h:3635:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> std::__cxx11::basic_string<_CharT, _Traits, _Allocator> std::operator+(_CharT, const __cxx11::basic_string<_CharT, _Traits, _Allocator>&)'
 3635 |     operator+(_CharT __lhs, const basic_string<_CharT,_Traits,_Alloc>& __rhs)
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3635:5: note:   template argument deduction/substitution failed:
a.cc:16:30: note:   mismatched types 'const std::__cxx11::basic_string<_CharT, _Traits, _Allocator>' and 'int'
   16 |         auto b_itr = a_itr + 1;
      |                              ^
/usr/include/c++/14/bits/basic_string.h:3652:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> std::__cxx11::basic_string<_CharT, _Traits, _Allocator> std::operator+(const __cxx11::basic_string<_CharT, _Traits, _Allocator>&, const _CharT*)'
 3652 |     operator+(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3652:5: note:   template argument deduction/substitution failed:
a.cc:16:30: note:   'std::_Rb_tree_const_iterator<long int>' is not derived from 'const std::__cxx11::basic_string<_CharT, _Traits, _Allocator>'
   16 |         auto b_itr = a_itr + 1;
      |                              ^
/usr/include/c++/14/bits/basic_string.h:3670:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> std::__cxx11::basic_string<_CharT, _Traits, _Allocator> std::operator+(const __cxx11::basic_string<_CharT, _Traits, _Allocator>&, _CharT)'
 3670 |     operator+(const basic_string<_CharT, _Traits, _Alloc>& __lhs, _CharT __rhs)
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3670:5: note:   template argument deduction/substitution failed:
a.cc:16:30: note:   'std::_Rb_tree_const_iterator<long int>' is not derived from 'const std::__cxx11::basic_string<_CharT, _Traits, _Allocator>'
   16 |         auto b_itr = a_itr + 1;
      |                              ^
/usr/include/c++/14/bits/basic_string.h:3682:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> std::__cxx11::basic_string<_CharT, _Traits, _Allocator> std::operator+(__cxx11::basic_string<_CharT, _Traits, _Allocator>&&, const __cxx11::basic_string<_CharT, _Traits, _Allocator>&)'
 3682 |     operator+(basic_string<_CharT, _Traits, _Alloc>&& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3682:5: note:   template argument deduction/substitution failed:
a.cc:16:30: note:   'std::_Rb_tree_const_iterator<long int>' is not derived from 'std::__cxx11::basic_string<_CharT, _Traits, _Allocator>'
   16 |         auto b_itr = a_itr + 1;
      |                              ^
/usr/include/c++/14/bits/basic_string.h:3689:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> std::__cxx11::basic_string<_CharT, _Traits, _Allocator> std::operator+(const __cxx11::basic_string<_CharT, _Traits, _Allocator>&, __cxx11::basic_string<_CharT, _Traits, _Allocator>&&)'
 3689 |     operator+(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3689:5: note:   template argument deduction/substitution failed:
a.cc:16:30: note:   'std::_Rb_tree_const_iterator<long int>' is not derived from 'const std::__cxx11::basic_string<_CharT, _Traits, _Allocator>'
   16 |         auto b_itr = a_itr + 1;
      |                              ^
/usr/include/c++/14/bits/basic_string.h:3696:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> std::__cxx11::basic_string<_CharT, _Traits, _Allocator> std::operator+(__cxx11::basic_string<_CharT, _Traits, _Allocator>&&, __cxx11::basic_string<_CharT, _Traits, _Allocator>&&)'
 3696 |     operator+(basic_string<_CharT, _Traits, _Alloc>&& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3696:5: note:   template argument deduction/substitution failed:
a.cc:16:30: note:   'std::_Rb_tree_const_iterator<long int>' is not derived from 'std::__cxx11::basic_string<_CharT, _Traits, _Allocator>'
   16 |         auto b_itr = a_itr + 1;
      |                              ^
/usr/include/c++/14/bits/basic_string.h:3719:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> std::__cxx11::basic_string<_CharT, _Traits, _Allocator> std::operator+(const _CharT*, __cxx11::basic_string<_CharT, _Traits, _Allocator>&&)'
 3719 |     operator+(const _CharT* __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3719:5: note:   template argument deduction/substitution failed:
a.cc:16:30: note:   mismatched types 'const _CharT*' and 'std::_Rb_tree_const_iterator<long int>'
   16 |         auto b_itr = a_itr + 1;
      |                              ^
/usr/include/c++/14/bits/basic_string.h:3726:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> std::__cxx11::basic_string<_CharT, _Traits, _Allocator> std::operator+(_CharT, __cxx11::basic_string<_CharT, _Traits, _Allocator>&&)'
 3726 |     operator+(_CharT __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3726:5: note:   template argument deduction/substitution failed:
a.cc:16:30: note:   mismatched types 'std::__cxx11::basic_string<_CharT, _Traits, _Allocator>' and 'int'
   16 |         auto b_itr = a_itr + 1;
      |                              ^
/usr/include/c++/14/bits/basic_string.h:3733:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> std::__cxx11::basic_string<_CharT, _Traits, _Allocator> std::operator+(__cxx11::basic_string<_CharT, _Traits, _Allocator>&&, const _CharT*)'
 3733 |     operator+(basic_string<_CharT, _Traits, _Alloc>&& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3733:5: note:   template argument deduction/substitution failed:
a.cc:16:30: note:   'std::_Rb_tree_const_iterator<long int>' is not derived from 'std::__cxx11::basic_string<_CharT, _Traits, _Allocator>'
   16 |         auto b_itr = a_itr + 1;
      |                              ^
/usr/include/c++/14/bits/basic_string.h:3740:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> std::__cxx11::basic_string<_CharT, _Traits, _Allocator> std::operator+(__cxx11::basic_string<_CharT, _Traits, _Allocator>&&, _CharT)'
 3740 |     operator+(basic_string<_CharT, _Traits, _Alloc>&& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3740:5: note:   template argument deduction/substitution failed:
a.cc:16:30: note:   'std::_Rb_tree_const_iterator<long int>' is not derived from 'std::__cxx11::basic_string<_CharT, _Traits, _Allocator>'
   16 |         auto b_itr = a_itr + 1;
      |                              ^
a.cc:21:28: error: 'c' was not declared in this scope
   21 |                 if(a + b > c && b + c > a && c + a > b){
      |