Language: C++

#include <iostream>
#include <cmath>
using namespace std;

double x0, y0, x1, y1;

int main() {
  cin>>x0>>y0>>x1>>y1;
  x1-=x0;
  y1-=y0;
  cout<<sqrt(x1*x1+y1*y1)<<endl;
  return 0;
}

Compiler output:
a.cc:5:12: error: 'double y0' redeclared as different kind of entity
    5 | double x0, y0, x1, y1;
      |            ^~
In file included from /usr/include/features.h:523,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/os_defines.h:39,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/c++config.h:683,
                 from /usr/include/c++/14/bits/requires_hosted.h:31,
                 from /usr/include/c++/14/iostream:38,
                 from a.cc:1:
/usr/include/x86_64-linux-gnu/bits/mathcalls.h:256:1: note: previous declaration 'double y0(double)'
  256 | __MATHCALL (y0,, (_Mdouble_));
      | ^~~~~~~~~~
a.cc:5:20: error: 'double y1' redeclared as different kind of entity
    5 | double x0, y0, x1, y1;
      |                    ^~
/usr/include/x86_64-linux-gnu/bits/mathcalls.h:257:1: note: previous declaration 'double y1(double)'
  257 | __MATHCALL (y1,, (_Mdouble_));
      | ^~~~~~~~~~
a.cc: In function 'int main()':
a.cc:8:10: error: no match for 'operator>>' (operand types are 'std::basic_istream<char>::__istream_type' {aka 'std::basic_istream<char>'} and 'double(double) noexcept')
    8 |   cin>>x0>>y0>>x1>>y1;
      |   ~~~~~~~^~~~
      |      |     |
      |      |     double(double) noexcept
      |      std::basic_istream<char>::__istream_type {aka std::basic_istream<char>}
In file included from /usr/include/c++/14/iostream:42:
/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:8:12: error: cannot bind non-const lvalue reference of type 'bool&' to a value of type 'double (*)(double) noexcept'
    8 |   cin>>x0>>y0>>x1>>y1;
      |            ^~
/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:8:12: error: invalid conversion from 'double (*)(double) noexcept' to 'short int' [-fpermissive]
    8 |   cin>>x0>>y0>>x1>>y1;
      |            ^~
      |            |
      |            double (*)(double) noexcept
a.cc:8:12: error: cannot bind rvalue '(short int)y0' 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:8:12: error: invalid conversion from 'double (*)(double) noexcept' to 'short unsigned int' [-fpermissive]
    8 |   cin>>x0>>y0>>x1>>y1;
      |            ^~
      |            |
      |            double (*)(double) noexcept
a.cc:8:12: error: cannot bind rvalue '(short unsigned int)y0' 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:8:12: error: invalid conversion from 'double (*)(double) noexcept' to 'int' [-fpermissive]
    8 |   cin>>x0>>y0>>x1>>y1;
      |            ^~
      |            |
      |            double (*)(double) noexcept
a.cc:8:12: error: cannot bind rvalue '(int)y0' 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:8:12: error: invalid conversion from 'double (*)(double) noexcept' to 'unsigned int' [-fpermissive]
    8 |   cin>>x0>>y0>>x1>>y1;
      |            ^~
      |            |
      |            double (*)(double) noexcept
a.cc:8:12: error: cannot bind rvalue '(unsigned int)y0' 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:8:12: error: invalid conversion from 'double (*)(double) noexcept' to 'long int' [-fpermissive]
    8 |   cin>>x0>>y0>>x1>>y1;
      |            ^~
      |            |
      |            double (*)(double) noexcept
a.cc:8:12: error: cannot bind rvalue '(long int)y0' 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:8:12: error: invalid conversion from 'double (*)(double) noexcept' to 'long unsigned int' [-fpermissive]
    8 |   cin>>x0>>y0>>x1>>y1;
      |            ^~
      |            |
      |            double (*)(double) noexcept
a.cc:8:12: error: cannot bind rvalue '(long unsigned int)y0' 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:8:12: error: invalid conversion from 'double (*)(double) noexcept' to 'long long int' [-fpermissive]
    8 |   cin>>x0>>y0>>x1>>y1;
      |            ^~
      |            |
      |            double (*)(double) noexcept
a.cc:8:12: error: cannot bind rvalue '(long long int)y0' 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:8:12: error: invalid conversion from 'double (*)(double) noexcept' to 'long long unsigned int' [-fpermissive]
    8 |   cin>>x0>>y0>>x1>>y1;
      |            ^~
      |            |
      |            double (*)(double) noexcept
a.cc:8:12: error: cannot bind rvalue '(long long unsigned int)y0' 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:8:12: error: invalid conversion from 'double (*)(double) noexcept' to 'void*' [-fpermissive]
    8 |   cin>>x0>>y0>>x1>>y1;
      |            ^~
      |            |
      |            double (*)(double) noexcept
a.cc:8:12: error: cannot bind rvalue '(void*)y0' 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:8:12: error: invalid conversion from 'double (*)(double) noexcept' to 'std::basic_istream<char>::__istream_type& (*)(std::basic_istream<char>::__istream_type&)' {aka 'std::basic_istream<char>& (*)(std::basic_istream<char>&)'} [-fpermissive]
    8 |   cin>>x0>>y0>>x1>>y1;
      |            ^~
      |            |
      |            double (*)(double) noexcept
/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:8:12: error: invalid conversion from 'double (*)(double) noexcept' to 'std::basic_istream<char>::__ios_type& (*)(std::basic_istream<char>::__ios_type&)' {aka 'std::basic_ios<char>& (*)(std::basic_ios<char>&)'} [-fpermissive]
    8 |   cin>>x0>>y0>>x1>>y1;
      |            ^~
      |            |
      |            double (*)(double) noexcept
/usr/include/c++/14/istream:133:7: note: candidat