Language: C++

#include <cstdio>
#include <cmath>
#include <cstring>
#include <cstdlib>
#include <climits>
#include <ctime>
#include <queue>
#include <stack>
#include <algorithm>
#include <list>
#include <vector>
#include <set>
#include <map>
#include <iostream>
#include <deque>
#include <complex>
#include <string>
#include <iomanip>
#include <sstream>
#include <bitset>
#include <valarray>
#include <iterator>
using namespace std;
typedef long long int ll;
typedef unsigned int uint;
typedef unsigned char uchar;
typedef unsigned long long ull;
typedef pair<int, int> pii;
typedef vector<int> vi;

#define REP(i,x) for(int i=0;i<(int)(x);i++)
#define FOR(i,c) for(__typeof((c).begin())i=(c).begin();i!=(c).end();i++)
#define RREP(i,x) for(int i=((int)(x)-1);i>=0;i--)
#define RFOR(i,c) for(__typeof((c).rbegin())i=(c).rbegin();i!=(c).rend();i++)
#define ALL(container) container.begin(), container.end()
#define RALL(container) container.rbegin(), container.rend()
#define SZ(container) ((int)container.size())
#define mp(a,b) make_pair(a, b)
#define UNIQUE(v) v.erase( unique(v.begin(), v.end()), v.end() );

template<class T> bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T> bool chmin(T &a, const T &b) { if (a>b) { a=b; return 1; } return 0; }
template<class T> ostream& operator<<(ostream &os, const vector<T> &t) {
os<<"["; FOR(it,t) {if(it!=t.begin()) os<<","; os<<*it;} os<<"]"; return os;
}
template<class T> ostream& operator<<(ostream &os, const set<T> &t) {
os<<"{"; FOR(it,t) {if(it!=t.begin()) os<<","; os<<*it;} os<<"}"; return os;
}
template<class S, class T> ostream& operator<<(ostream &os, const pair<S,T> &t) { return os<<"("<<t.first<<","<<t.second<<")";}

const int INF = 1<<28;
const double EPS = 1e-8;
const int MOD = 1000000007;


int n, m;
string str;
main(){
	cin >> str;
	reverse(ALL(str));
	cout << str < endl;
	return 0;
}

Compiler output:
a.cc:58:1: warning: ISO C++ forbids declaration of 'main' with no type [-Wreturn-type]
   58 | main(){
      | ^~~~
a.cc: In function 'int main()':
a.cc:61:21: error: no match for 'operator<' (operand types are 'std::basic_ostream<char>' and '<unresolved overloaded function type>')
   61 |         cout << str < endl;
      |         ~~~~~~~~~~~~^~~~~~
In file included from /usr/include/c++/14/bits/stl_algobase.h:64,
                 from /usr/include/c++/14/bits/specfun.h:43,
                 from /usr/include/c++/14/cmath:3906,
                 from a.cc:2:
/usr/include/c++/14/bits/stl_pair.h:1045:5: note: candidate: 'template<class _T1, class _T2> constexpr bool std::operator<(const pair<_T1, _T2>&, const pair<_T1, _T2>&)'
 1045 |     operator<(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_pair.h:1045:5: note:   template argument deduction/substitution failed:
a.cc:61:23: note:   'std::basic_ostream<char>' is not derived from 'const std::pair<_T1, _T2>'
   61 |         cout << str < endl;
      |                       ^~~~
In file included from /usr/include/c++/14/bits/stl_algobase.h:67:
/usr/include/c++/14/bits/stl_iterator.h:448:5: note: candidate: 'template<class _Iterator> constexpr bool std::operator<(const reverse_iterator<_Iterator>&, const reverse_iterator<_Iterator>&)'
  448 |     operator<(const reverse_iterator<_Iterator>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:448:5: note:   template argument deduction/substitution failed:
a.cc:61:23: note:   'std::basic_ostream<char>' is not derived from 'const std::reverse_iterator<_Iterator>'
   61 |         cout << str < endl;
      |                       ^~~~
/usr/include/c++/14/bits/stl_iterator.h:493:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr bool std::operator<(const reverse_iterator<_Iterator>&, const reverse_iterator<_IteratorR>&)'
  493 |     operator<(const reverse_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:493:5: note:   template argument deduction/substitution failed:
a.cc:61:23: note:   'std::basic_ostream<char>' is not derived from 'const std::reverse_iterator<_Iterator>'
   61 |         cout << str < endl;
      |                       ^~~~
/usr/include/c++/14/bits/stl_iterator.h:1694:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr bool std::operator<(const move_iterator<_IteratorL>&, const move_iterator<_IteratorR>&)'
 1694 |     operator<(const move_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1694:5: note:   template argument deduction/substitution failed:
a.cc:61:23: note:   'std::basic_ostream<char>' is not derived from 'const std::move_iterator<_IteratorL>'
   61 |         cout << str < endl;
      |                       ^~~~
/usr/include/c++/14/bits/stl_iterator.h:1760:5: note: candidate: 'template<class _Iterator> constexpr bool std::operator<(const move_iterator<_IteratorL>&, const move_iterator<_IteratorL>&)'
 1760 |     operator<(const move_iterator<_Iterator>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1760:5: note:   template argument deduction/substitution failed:
a.cc:61:23: note:   'std::basic_ostream<char>' is not derived from 'const std::move_iterator<_IteratorL>'
   61 |         cout << str < endl;
      |                       ^~~~
In file included from /usr/include/c++/14/deque:66,
                 from /usr/include/c++/14/queue:62,
                 from a.cc:7:
/usr/include/c++/14/bits/stl_deque.h:2334:5: note: candidate: 'template<class _Tp, class _Alloc> bool std::operator<(const deque<_Tp, _Alloc>&, const deque<_Tp, _Alloc>&)'
 2334 |     operator<(const deque<_Tp, _Alloc>& __x, const deque<_Tp, _Alloc>& __y)
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_deque.h:2334:5: note:   template argument deduction/substitution failed:
a.cc:61:23: note:   'std::basic_ostream<char>' is not derived from 'const std::deque<_Tp, _Alloc>'
   61 |         cout << str < endl;
      |                       ^~~~
In file included from /usr/include/c++/14/bits/memory_resource.h:47,
                 from /usr/include/c++/14/deque:81:
/usr/include/c++/14/tuple:2600:5: note: candidate: 'template<class ... _TElements, class ... _UElements> constexpr bool std::operator<(const tuple<_UTypes ...>&, const tuple<_Elements ...>&)'
 2600 |     operator<(const tuple<_TElements...>& __t,
      |     ^~~~~~~~
/usr/include/c++/14/tuple:2600:5: note:   template argument deduction/substitution failed:
a.cc:61:23: note:   'std::basic_ostream<char>' is not derived from 'const std::tuple<_UTypes ...>'
   61 |         cout << str < endl;
      |                       ^~~~
In file included from /usr/include/c++/14/vector:66,
                 from /usr/include/c++/14/queue:63:
/usr/include/c++/14/bits/stl_vector.h:2089:5: note: candidate: 'template<class _Tp, class _Alloc> bool std::operator<(const vector<_Tp, _Alloc>&, const vector<_Tp, _Alloc>&)'
 2089 |     operator<(const vector<_Tp, _Alloc>& __x, const vector<_Tp, _Alloc>& __y)
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_vector.h:2089:5: note:   template argument deduction/substitution failed:
a.cc:61:23: note:   'std::basic_ostream<char>' is not derived from 'const std::vector<_Tp, _Alloc>'
   61 |         cout << str < endl;
      |                       ^~~~
In file included from /usr/include/c++/14/queue:66:
/usr/include/c++/14/bits/stl_queue.h:397:5: note: candidate: 'template<class _Tp, class _Seq> bool std::operator<(const queue<_Tp, _Seq>&, const queue<_Tp, _Seq>&)'
  397 |     operator<(const queue<_Tp, _Seq>& __x, const queue<_Tp, _Seq>& __y)
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_queue.h:397:5: note:   template argument deduction/substitution failed:
a.cc:61:23: note:   'std::basic_ostream<char>' is not derived from 'const std::queue<_Tp, _Seq>'
   61 |         cout << str < endl;
      |                       ^~~~
In file included from /usr/include/c++/14/stack:63,
                 from a.cc:8:
/usr/include/c++/14/bits/stl_stack.h:373:5: note: candidate: 'template<class _Tp, class _Seq> bool std::operator<(const stack<_Tp, _Seq>&, const stack<_Tp, _Seq>&)'
  373 |     operator<(const stack<_Tp, _Seq>& __x, const stack<_Tp, _Seq>& __y)
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_stack.h:373:5: note:   template argument deduction/substitution failed:
a.cc:61:23: note:   'std::basic_ostream<char>' is not derived from 'const std::stack<_Tp, _Seq>'
   61 |         cout << str < endl;
      |                       ^~~~
In file included from /usr/include/c++/14/list:65,
                 from a.cc:10:
/usr/include/c++/14/bits/stl_list.h:2188:5: note: candidate: 'template<class _Tp, class _Alloc> bool std::operator<(const __cxx11::list<_Tp, _Alloc>&, const __cxx11::list<_Tp, _Alloc>&)'
 2188 |     operator<(const list<_Tp, _Alloc>& __x, const list<_Tp, _Alloc>& __y)
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_list.h:2188:5: note:   template argument deduction/substitution failed:
a.cc:61:23: note:   'std::basic_ostream<char>' is not derived from 'const std::__cxx11::list<_Tp, _Alloc>'
   61 |         cout << str < endl;
      |                       ^~~~
In file included from /usr/include/c++/14/set:63,
                 from a.cc:12:
/usr/include/c++/14/bits/stl_set.h:1025:5: note: candidate: 'template<class _Key, class _Compare, class _Alloc> bool std::operator<(const set<_Key, _Compare, _Allocator>&, const set<_Key, _Compare, _Allocator>&)'
 1025 |     operator<(const set<_Key, _Compare, _Alloc>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_set.h:1025:5: note:   template argument deduction/substitution failed:
a.cc:61:23: note:   'std::basic_ostream<char>' is not derived from 'const std::set<_Key, _Compare, _Allocator>'
   61 |         cout << str < endl;
      |                       ^~~~
In file included from /usr/include/c++/14/set:64:
/usr/include/c++/14/bits/stl_multiset.h:1011:5: note: candidate: 'template<class _Key, class _Compare, class _Alloc> bool std::operator<(const multiset<_Key, _Compare, _Allocator>&, const multiset<_Key, _Compare, _Allocator>&)'
 1011 |     operator<(const multiset<_Key, _Compare, _Alloc>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_multiset.h:1011:5: note:   template argument deduction/substitution failed:
a.cc:61:23: note:   'std::basic_ostream<char>' is not derived from 'const std::multiset<_Key, _Compare, _Allocator>'
   61 |         cout << str < endl;
      |                       ^~~~
In file included from /usr/include/c++/14/map:63,
                 from a.cc:13:
/usr/include/c++/14/bits/stl_map.h:1550:5: note: candidate: 'template<class _Key, class _Tp, class _Compare, class _Alloc> bool std::operator<(const map<_Key, _Tp, _Compare, _Allocator>&, const map<_Key, _Tp, _Compare, _Allocator>&)'
 1550 |     operator<(const map<_Key, _Tp, _Compare, _Alloc>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_map.h:1550:5: note:   template argument deduction/substitution failed:
a.cc:61:23: note:   'std::basic_ostream<char>' is not derived from 'const std::map<_Key, _Tp, _Compare, _Allocator>'
   61 |         cout << str < endl;
      |                       ^~~~
In file included from /usr/include/c++/14/map:64:
/usr/include/c++/14/bits/stl_multimap.h:1172:5: note: candidate: 'template<class _Key, class _Tp, class _Compare, class _Alloc> bool std::operator<(const multimap<_Key, _Tp, _Compare, _Allocator>&, const multimap<_Key, _Tp, _Compare, _Allocator>&)'
 1172 |     operator<(const multimap<_Key, _Tp, _Compare, _Alloc>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_multimap.h:1172:5: note:   template argument deduction/substitution failed:
a.cc:61:23: note:   'std::basic_ostream<char>' is not derived from 'const std::multimap<_Key, _Tp, _Compare, _Allocator>'
   61 |         cout << str < endl;
      |                       ^~~~
In file included from /usr/include/c++/14/bits/basic_string.h:47,
                 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,