Language: C++

#include<iostream>
#include<string>

using namespace std;

int main(void)
{
  string s();
  
  cin>>s;
  
  int size=s.size();
  int right=size;
  int ans=0;
  
  for(int i=0;i<size;i++)
  {
    if(s[i] != s[right])
      ans++;
    
    right--;
    if(i==right)
        break;
  }
  
  cout<<ans<<endl;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:8:11: warning: empty parentheses were disambiguated as a function declaration [-Wvexing-parse]
    8 |   string s();
      |           ^~
a.cc:8:11: note: remove parentheses to default-initialize a variable
    8 |   string s();
      |           ^~
      |           --
a.cc:10:6: error: no match for 'operator>>' (operand types are 'std::istream' {aka 'std::basic_istream<char>'} and 'std::string()' {aka 'std::__cxx11::basic_string<char>()'})
   10 |   cin>>s;
      |   ~~~^~~
      |   |    |
      |   |    std::string() {aka std::__cxx11::basic_string<char>()}
      |   std::istream {aka std::basic_istream<char>}
In file included from /usr/include/c++/14/iostream:42,
                 from a.cc:1:
/usr/include/c++/14/istream:170:7: note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(bool&) [with _CharT = char; _Traits = std::char_traits<char>; __istream_type = std::basic_istream<char>]' (near match)
  170 |       operator>>(bool& __n)
      |       ^~~~~~~~
/usr/include/c++/14/istream:170:7: note:   conversion of argument 1 would be ill-formed:
a.cc:10:8: error: cannot bind non-const lvalue reference of type 'bool&' to a value of type 'std::string (*)()' {aka 'std::__cxx11::basic_string<char> (*)()'}
   10 |   cin>>s;
      |        ^
/usr/include/c++/14/istream:174:7: note: candidate: 'std::basic_istream<_CharT, _Traits>& std::basic_istream<_CharT, _Traits>::operator>>(short int&) [with _CharT = char; _Traits = std::char_traits<char>]' (near match)
  174 |       operator>>(short& __n);
      |       ^~~~~~~~
/usr/include/c++/14/istream:174:7: note:   conversion of argument 1 would be ill-formed:
a.cc:10:8: error: invalid conversion from 'std::string (*)()' {aka 'std::__cxx11::basic_string<char> (*)()'} to 'short int' [-fpermissive]
   10 |   cin>>s;
      |        ^
      |        |
      |        std::string (*)() {aka std::__cxx11::basic_string<char> (*)()}
a.cc:10:8: error: cannot bind rvalue '(short int)s' to 'short int&'
/usr/include/c++/14/istream:177:7: note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(short unsigned int&) [with _CharT = char; _Traits = std::char_traits<char>; __istream_type = std::basic_istream<char>]' (near match)
  177 |       operator>>(unsigned short& __n)
      |       ^~~~~~~~
/usr/include/c++/14/istream:177:7: note:   conversion of argument 1 would be ill-formed:
a.cc:10:8: error: invalid conversion from 'std::string (*)()' {aka 'std::__cxx11::basic_string<char> (*)()'} to 'short unsigned int' [-fpermissive]
   10 |   cin>>s;
      |        ^
      |        |
      |        std::string (*)() {aka std::__cxx11::basic_string<char> (*)()}
a.cc:10:8: error: cannot bind rvalue '(short unsigned int)s' to 'short unsigned int&'
/usr/include/c++/14/istream:181:7: note: candidate: 'std::basic_istream<_CharT, _Traits>& std::basic_istream<_CharT, _Traits>::operator>>(int&) [with _CharT = char; _Traits = std::char_traits<char>]' (near match)
  181 |       operator>>(int& __n);
      |       ^~~~~~~~
/usr/include/c++/14/istream:181:7: note:   conversion of argument 1 would be ill-formed:
a.cc:10:8: error: invalid conversion from 'std::string (*)()' {aka 'std::__cxx11::basic_string<char> (*)()'} to 'int' [-fpermissive]
   10 |   cin>>s;
      |        ^
      |        |
      |        std::string (*)() {aka std::__cxx11::basic_string<char> (*)()}
a.cc:10:8: error: cannot bind rvalue '(int)s' to 'int&'
/usr/include/c++/14/istream:184:7: note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(unsigned int&) [with _CharT = char; _Traits = std::char_traits<char>; __istream_type = std::basic_istream<char>]' (near match)
  184 |       operator>>(unsigned int& __n)
      |       ^~~~~~~~
/usr/include/c++/14/istream:184:7: note:   conversion of argument 1 would be ill-formed:
a.cc:10:8: error: invalid conversion from 'std::string (*)()' {aka 'std::__cxx11::basic_string<char> (*)()'} to 'unsigned int' [-fpermissive]
   10 |   cin>>s;
      |        ^
      |        |
      |        std::string (*)() {aka std::__cxx11::basic_string<char> (*)()}
a.cc:10:8: error: cannot bind rvalue '(unsigned int)s' to 'unsigned int&'
/usr/include/c++/14/istream:188:7: note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(long int&) [with _CharT = char; _Traits = std::char_traits<char>; __istream_type = std::basic_istream<char>]' (near match)
  188 |       operator>>(long& __n)
      |       ^~~~~~~~
/usr/include/c++/14/istream:188:7: note:   conversion of argument 1 would be ill-formed:
a.cc:10:8: error: invalid conversion from 'std::string (*)()' {aka 'std::__cxx11::basic_string<char> (*)()'} to 'long int' [-fpermissive]
   10 |   cin>>s;
      |        ^
      |        |
      |        std::string (*)() {aka std::__cxx11::basic_string<char> (*)()}
a.cc:10:8: error: cannot bind rvalue '(long int)s' to 'long int&'
/usr/include/c++/14/istream:192:7: note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(long unsigned int&) [with _CharT = char; _Traits = std::char_traits<char>; __istream_type = std::basic_istream<char>]' (near match)
  192 |       operator>>(unsigned long& __n)
      |       ^~~~~~~~
/usr/include/c++/14/istream:192:7: note:   conversion of argument 1 would be ill-formed:
a.cc:10:8: error: invalid conversion from 'std::string (*)()' {aka 'std::__cxx11::basic_string<char> (*)()'} to 'long unsigned int' [-fpermissive]
   10 |   cin>>s;
      |        ^
      |        |
      |        std::string (*)() {aka std::__cxx11::basic_string<char> (*)()}
a.cc:10:8: error: cannot bind rvalue '(long unsigned int)s' to 'long unsigned int&'
/usr/include/c++/14/istream:199:7: note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(long long int&) [with _CharT = char; _Traits = std::char_traits<char>; __istream_type = std::basic_istream<char>]' (near match)
  199 |       operator>>(long long& __n)
      |       ^~~~~~~~
/usr/include/c++/14/istream:199:7: note:   conversion of argument 1 would be ill-formed:
a.cc:10:8: error: invalid conversion from 'std::string (*)()' {aka 'std::__cxx11::basic_string<char> (*)()'} to 'long long int' [-fpermissive]
   10 |   cin>>s;
      |        ^
      |        |
      |        std::string (*)() {aka std::__cxx11::basic_string<char> (*)()}
a.cc:10:8: error: cannot bind rvalue '(long long int)s' to 'long long int&'
/usr/include/c++/14/istream:203:7: note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(long long unsigned int&) [with _CharT = char; _Traits = std::char_traits<char>; __istream_type = std::basic_istream<char>]' (near match)
  203 |       operator>>(unsigned long long& __n)
      |       ^~~~~~~~
/usr/include/c++/14/istream:203:7: note:   conversion of argument 1 would be ill-formed:
a.cc:10:8: error: invalid conversion from 'std::string (*)()' {aka 'std::__cxx11::basic_string<char> (*)()'} to 'long long unsigned int' [-fpermissive]
   10 |   cin>>s;
      |        ^
      |        |
      |        std::string (*)() {aka std::__cxx11::basic_string<char> (*)()}
a.cc:10:8: error: cannot bind rvalue '(long long unsigned int)s' to 'long long unsigned int&'
/usr/include/c++/14/istream:328:7: note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(void*&) [with _CharT = char; _Traits = std::char_traits<char>; __istream_type = std::basic_istream<char>]' (near match)
  328 |       operator>>(void*& __p)
      |       ^~~~~~~~
/usr/include/c++/14/istream:328:7: note:   conversion of argument 1 would be ill-formed:
a.cc:10:8: error: invalid conversion from 'std::string (*)()' {aka 'std::__cxx11::basic_string<char> (*)()'} to 'void*' [-fpermissive]
   10 |   cin>>s;
      |        ^
      |        |
      |        std::string (*)() {aka std::__cxx11::basic_string<char> (*)()}
a.cc:10:8: error: cannot bind rvalue '(void*)s' to 'void*&'
/usr/include/c++/14/istream:122:7: note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(__istream_type& (*)(__istream_type&)) [with _CharT = char; _Traits = std::char_traits<char>; __istream_type = std::basic_istream<char>]' (near match)
  122 |       operator>>(__istream_type& (*__pf)(__istream_type&))
      |       ^~~~~~~~
/usr/include/c++/14/istream:122:7: note:   conversion of argument 1 would be ill-formed:
a.cc:10:8: error: invalid conversion from 'std::string (*)()' {aka 'std::__cxx11::basic_string<char> (*)()'} to 'std::basic_istream<char>::__istream_type& (*)(std::basic_istream<char>::__istream_type&)' {aka 'std::basic_istream<char>& (*)(std::basic_istream<char>&)'} [-fpermissive]
   10 |   cin>>s;
      |        ^
      |        |
      |        std::string (*)() {aka std::__cxx11::basic_string<char> (*)()}
/usr/include/c++/14/istream:126:7: note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(__ios_type& (*)(__ios_type&)) [with _CharT = char; _Traits = std::char_traits<char>; __istream_type = std::basic_istream<char>; __ios_type = std::basic_ios<char>]' (near match)
  126 |       operator>>(__ios_type& (*__pf)(__ios_type&))
      |       ^~~~~~~~
/usr/include/c++/14/istream:126:7: note:   conversion of argument 1 would be ill-formed:
a.cc:10:8: error: invalid conversion from 'std::string (*)()' {aka 'std::__cxx11::basic_string<char> (*)()'} to 'std::basic_istream<char>::__ios_type& (*)(std::basic_istream<char>::__ios_type&)' {aka 'std::basic_ios<char>& (*)(std::basic_ios<char>&)'} [-fpermissive]
   10 |   cin>>s;
      |        ^
      |        |
      |        std::string (*)() {aka std::__cxx11::basic_string<char> (*)()}
/usr/include/c++/14/istream:133:7: note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(std::ios_base& (*)(std::ios_bas