Language: C++

#include<cstdio>
#include<iostream>
#include<string>

using namespace std;

int main(void) {

	string a, b, c;

	cin >> a >> b >> c;

	if (a.at(a.end()) == b.at(b.begin()) && b.at(b.end()) == c.at(c.begin())) {
		cout << "YES\n";
	}
	else {
		cout << "NO\n";
	}

	return 0;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:13:17: error: no matching function for call to 'std::__cxx11::basic_string<char>::at(std::__cxx11::basic_string<char>::iterator)'
   13 |         if (a.at(a.end()) == b.at(b.begin()) && b.at(b.end()) == c.at(c.begin())) {
      |             ~~~~^~~~~~~~~
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:2:
/usr/include/c++/14/bits/basic_string.h:1287:7: note: candidate: 'std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::const_reference std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::at(size_type) const [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>; const_reference = const char&; size_type = long unsigned int]'
 1287 |       at(size_type __n) const
      |       ^~
/usr/include/c++/14/bits/basic_string.h:1287:20: note:   no known conversion for argument 1 from 'std::__cxx11::basic_string<char>::iterator' to 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'}
 1287 |       at(size_type __n) const
      |          ~~~~~~~~~~^~~
/usr/include/c++/14/bits/basic_string.h:1309:7: note: candidate: 'std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::reference std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::at(size_type) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>; reference = char&; size_type = long unsigned int]'
 1309 |       at(size_type __n)
      |       ^~
/usr/include/c++/14/bits/basic_string.h:1309:20: note:   no known conversion for argument 1 from 'std::__cxx11::basic_string<char>::iterator' to 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'}
 1309 |       at(size_type __n)
      |          ~~~~~~~~~~^~~
a.cc:13:34: error: no matching function for call to 'std::__cxx11::basic_string<char>::at(std::__cxx11::basic_string<char>::iterator)'
   13 |         if (a.at(a.end()) == b.at(b.begin()) && b.at(b.end()) == c.at(c.begin())) {
      |                              ~~~~^~~~~~~~~~~
/usr/include/c++/14/bits/basic_string.h:1287:7: note: candidate: 'std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::const_reference std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::at(size_type) const [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>; const_reference = const char&; size_type = long unsigned int]'
 1287 |       at(size_type __n) const
      |       ^~
/usr/include/c++/14/bits/basic_string.h:1287:20: note:   no known conversion for argument 1 from 'std::__cxx11::basic_string<char>::iterator' to 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'}
 1287 |       at(size_type __n) const
      |          ~~~~~~~~~~^~~
/usr/include/c++/14/bits/basic_string.h:1309:7: note: candidate: 'std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::reference std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::at(size_type) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>; reference = char&; size_type = long unsigned int]'
 1309 |       at(size_type __n)
      |       ^~
/usr/include/c++/14/bits/basic_string.h:1309:20: note:   no known conversion for argument 1 from 'std::__cxx11::basic_string<char>::iterator' to 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'}
 1309 |       at(size_type __n)
      |          ~~~~~~~~~~^~~
a.cc:13:53: error: no matching function for call to 'std::__cxx11::basic_string<char>::at(std::__cxx11::basic_string<char>::iterator)'
   13 |         if (a.at(a.end()) == b.at(b.begin()) && b.at(b.end()) == c.at(c.begin())) {
      |                                                 ~~~~^~~~~~~~~
/usr/include/c++/14/bits/basic_string.h:1287:7: note: candidate: 'std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::const_reference std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::at(size_type) const [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>; const_reference = const char&; size_type = long unsigned int]'
 1287 |       at(size_type __n) const
      |       ^~
/usr/include/c++/14/bits/basic_string.h:1287:20: note:   no known conversion for argument 1 from 'std::__cxx11::basic_string<char>::iterator' to 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'}
 1287 |       at(size_type __n) const
      |          ~~~~~~~~~~^~~
/usr/include/c++/14/bits/basic_string.h:1309:7: note: candidate: 'std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::reference std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::at(size_type) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>; reference = char&; size_type = long unsigned int]'
 1309 |       at(size_type __n)
      |       ^~
/usr/include/c++/14/bits/basic_string.h:1309:20: note:   no known conversion for argument 1 from 'std::__cxx11::basic_string<char>::iterator' to 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'}
 1309 |       at(size_type __n)
      |          ~~~~~~~~~~^~~
a.cc:13:70: error: no matching function for call to 'std::__cxx11::basic_string<char>::at(std::__cxx11::basic_string<char>::iterator)'
   13 |         if (a.at(a.end()) == b.at(b.begin()) && b.at(b.end()) == c.at(c.begin())) {
      |                                                                  ~~~~^~~~~~~~~~~
/usr/include/c++/14/bits/basic_string.h:1287:7: note: candidate: 'std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::const_reference std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::at(size_type) const [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>; const_reference = const char&; size_type = long unsigned int]'
 1287 |       at(size_type __n) const
      |       ^~
/usr/include/c++/14/bits/basic_string.h:1287:20: note:   no known conversion for argument 1 from 'std::__cxx11::basic_string<char>::iterator' to 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'}
 1287 |       at(size_type __n) const
      |          ~~~~~~~~~~^~~
/usr/include/c++/14/bits/basic_string.h:1309:7: note: candidate: 'std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::reference std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::at(size_type) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>; reference = char&; size_type = long unsigned int]'
 1309 |       at(size_type __n)
      |       ^~
/usr/include/c++/14/bits/basic_string.h:1309:20: note:   no known conversion for argument 1 from 'std::__cxx11::basic_string<char>::iterator' to 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'}
 1309 |       at(size_type __n)
      |          ~~~~~~~~~~^~~