Language: C++

#include <iostream>
#include <string>
using namespace std;
int main(){
  string s1,s2;
  cin >> s1 >> s2;
  s1.append();
  if(s1==s2){
    cout << "Yes" << endl;
  }
  else{
    cout << "No" << endl;
      }
}


Compiler output:
a.cc: In function 'int main()':
a.cc:7:12: error: no matching function for call to 'std::__cxx11::basic_string<char>::append()'
    7 |   s1.append();
      |   ~~~~~~~~~^~
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:1529:9: note: candidate: 'template<class _InputIterator, class> std::__cxx11::basic_string<_CharT, _Traits, _Alloc>& std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::append(_InputIterator, _InputIterator) [with <template-parameter-2-2> = _InputIterator; _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>]'
 1529 |         append(_InputIterator __first, _InputIterator __last)
      |         ^~~~~~
/usr/include/c++/14/bits/basic_string.h:1529:9: note:   candidate expects 2 arguments, 0 provided
/usr/include/c++/14/bits/basic_string.h:1541:9: note: candidate: 'template<class _Tp> std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::_If_sv<_Tp, std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&> std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::append(const _Tp&) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>]'
 1541 |         append(const _Tp& __svt)
      |         ^~~~~~
/usr/include/c++/14/bits/basic_string.h:1541:9: note:   candidate expects 1 argument, 0 provided
/usr/include/c++/14/bits/basic_string.h:1557:9: note: candidate: 'template<class _Tp> std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::_If_sv<_Tp, std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&> std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::append(const _Tp&, size_type, size_type) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>]'
 1557 |         append(const _Tp& __svt, size_type __pos, size_type __n = npos)
      |         ^~~~~~
/usr/include/c++/14/bits/basic_string.h:1557:9: note:   candidate expects 2 arguments, 0 provided
/usr/include/c++/14/bits/basic_string.h:1435:7: note: candidate: 'std::__cxx11::basic_string<_CharT, _Traits, _Alloc>& std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::append(const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>]'
 1435 |       append(const basic_string& __str)
      |       ^~~~~~
/usr/include/c++/14/bits/basic_string.h:1435:7: note:   candidate expects 1 argument, 0 provided
/usr/include/c++/14/bits/basic_string.h:1453:7: note: candidate: 'std::__cxx11::basic_string<_CharT, _Traits, _Alloc>& std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::append(const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&, size_type, size_type) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>; size_type = long unsigned int]'
 1453 |       append(const basic_string& __str, size_type __pos, size_type __n = npos)
      |       ^~~~~~
/usr/include/c++/14/bits/basic_string.h:1453:7: note:   candidate expects 3 arguments, 0 provided
/usr/include/c++/14/bits/basic_string.h:1466:7: note: candidate: 'std::__cxx11::basic_string<_CharT, _Traits, _Alloc>& std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::append(const _CharT*, size_type) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>; size_type = long unsigned int]'
 1466 |       append(const _CharT* __s, size_type __n)
      |       ^~~~~~
/usr/include/c++/14/bits/basic_string.h:1466:7: note:   candidate expects 2 arguments, 0 provided
/usr/include/c++/14/bits/basic_string.h:1480:7: note: candidate: 'std::__cxx11::basic_string<_CharT, _Traits, _Alloc>& std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::append(const _CharT*) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>]'
 1480 |       append(const _CharT* __s)
      |       ^~~~~~
/usr/include/c++/14/bits/basic_string.h:1480:7: note:   candidate expects 1 argument, 0 provided
/usr/include/c++/14/bits/basic_string.h:1498:7: note: candidate: 'std::__cxx11::basic_string<_CharT, _Traits, _Alloc>& std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::append(size_type, _CharT) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>; size_type = long unsigned int]'
 1498 |       append(size_type __n, _CharT __c)
      |       ^~~~~~
/usr/include/c++/14/bits/basic_string.h:1498:7: note:   candidate expects 2 arguments, 0 provided
/usr/include/c++/14/bits/basic_string.h:1509:7: note: candidate: 'std::__cxx11::basic_string<_CharT, _Traits, _Alloc>& std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::append(std::initializer_list<_Tp>) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>]'
 1509 |       append(initializer_list<_CharT> __l)
      |       ^~~~~~
/usr/include/c++/14/bits/basic_string.h:1509:7: note:   candidate expects 1 argument, 0 provided