Language: C++

#include <iostream>

using namespace std;

class Point{
public:
	double x;
	double y;
	Point(double x=0,double y=0) :x(x),y(y){ }
	Point operator +(Point &p) {
		return Point(x + p.x, y + p.y);
	}
	Point operator-(Point &p) {
		return Point(x - p.x, y - p.y);
	}
	Point operator *(double a) {
		return Point(x*a, y*a);
	}
};

typedef struct {
	Point p1, p2;
}Line;

int main() {
	Line s;
	cin >> s.p1.x; cin >> s.p1.y; cin >> s.p2.x; cin >> s.p2.y;
	double q;
	cin >> q;
	for (double i = 0;i < q;i++) {
		Point p,q;
		cin >> p.x; cin >> p.y;
		double prod = ((s.p2.x - s.p1.x)*(p.x - s.p1.x)) + ((s.p2.y - s.p1.y)*(p.y - s.p1.y));
		q = s.p1 +(s.p2 - s.p1)*(prod/((s.p1.x-s.p2.x)*(s.p1.x - s.p2.x)+ (s.p1.y - s.p2.y)*(s.p1.y - s.p2.y)));
		cout << q.x << " " << q.y << endl;
	}

}

Compiler output:
a.cc: In function 'int main()':
a.cc:34:26: error: no match for 'operator+' (operand types are 'Point' and 'Point')
   34 |                 q = s.p1 +(s.p2 - s.p1)*(prod/((s.p1.x-s.p2.x)*(s.p1.x - s.p2.x)+ (s.p1.y - s.p2.y)*(s.p1.y - s.p2.y)));
      |                     ~~~~ ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      |                       |                |
      |                       Point            Point
a.cc:10:15: note: candidate: 'Point Point::operator+(Point&)' (near match)
   10 |         Point operator +(Point &p) {
      |               ^~~~~~~~
a.cc:10:15: note:   conversion of argument 1 would be ill-formed:
a.cc:34:40: error: cannot bind non-const lvalue reference of type 'Point&' to an rvalue of type 'Point'
   34 |                 q = s.p1 +(s.p2 - s.p1)*(prod/((s.p1.x-s.p2.x)*(s.p1.x - s.p2.x)+ (s.p1.y - s.p2.y)*(s.p1.y - s.p2.y)));
      |                           ~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /usr/include/c++/14/string:48,
                 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/stl_iterator.h:627:5: note: candidate: 'template<class _Iterator> constexpr std::reverse_iterator<_Iterator> std::operator+(typename reverse_iterator<_Iterator>::difference_type, const reverse_iterator<_Iterator>&)'
  627 |     operator+(typename reverse_iterator<_Iterator>::difference_type __n,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:627:5: note:   template argument deduction/substitution failed:
a.cc:34:119: note:   'Point' is not derived from 'const std::reverse_iterator<_Iterator>'
   34 |                 q = s.p1 +(s.p2 - s.p1)*(prod/((s.p1.x-s.p2.x)*(s.p1.x - s.p2.x)+ (s.p1.y - s.p2.y)*(s.p1.y - s.p2.y)));
      |                                                                                                                       ^
/usr/include/c++/14/bits/stl_iterator.h:1798:5: note: candidate: 'template<class _Iterator> constexpr std::move_iterator<_IteratorL> std::operator+(typename move_iterator<_IteratorL>::difference_type, const move_iterator<_IteratorL>&)'
 1798 |     operator+(typename move_iterator<_Iterator>::difference_type __n,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1798:5: note:   template argument deduction/substitution failed:
a.cc:34:119: note:   'Point' is not derived from 'const std::move_iterator<_IteratorL>'
   34 |                 q = s.p1 +(s.p2 - s.p1)*(prod/((s.p1.x-s.p2.x)*(s.p1.x - s.p2.x)+ (s.p1.y - s.p2.y)*(s.p1.y - s.p2.y)));
      |                                                                                                                       ^
In file included from /usr/include/c++/14/string:54:
/usr/include/c++/14/bits/basic_string.h:3598:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> std::__cxx11::basic_string<_CharT, _Traits, _Allocator> std::operator+(const __cxx11::basic_string<_CharT, _Traits, _Allocator>&, const __cxx11::basic_string<_CharT, _Traits, _Allocator>&)'
 3598 |     operator+(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3598:5: note:   template argument deduction/substitution failed:
a.cc:34:119: note:   'Point' is not derived from 'const std::__cxx11::basic_string<_CharT, _Traits, _Allocator>'
   34 |                 q = s.p1 +(s.p2 - s.p1)*(prod/((s.p1.x-s.p2.x)*(s.p1.x - s.p2.x)+ (s.p1.y - s.p2.y)*(s.p1.y - s.p2.y)));
      |                                                                                                                       ^
/usr/include/c++/14/bits/basic_string.h:3616:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> std::__cxx11::basic_string<_CharT, _Traits, _Allocator> std::operator+(const _CharT*, const __cxx11::basic_string<_CharT, _Traits, _Allocator>&)'
 3616 |     operator+(const _CharT* __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3616:5: note:   template argument deduction/substitution failed:
a.cc:34:119: note:   mismatched types 'const _CharT*' and 'Point'
   34 |                 q = s.p1 +(s.p2 - s.p1)*(prod/((s.p1.x-s.p2.x)*(s.p1.x - s.p2.x)+ (s.p1.y - s.p2.y)*(s.p1.y - s.p2.y)));
      |                                                                                                                       ^
/usr/include/c++/14/bits/basic_string.h:3635:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> std::__cxx11::basic_string<_CharT, _Traits, _Allocator> std::operator+(_CharT, const __cxx11::basic_string<_CharT, _Traits, _Allocator>&)'
 3635 |     operator+(_CharT __lhs, const basic_string<_CharT,_Traits,_Alloc>& __rhs)
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3635:5: note:   template argument deduction/substitution failed:
a.cc:34:119: note:   'Point' is not derived from 'const std::__cxx11::basic_string<_CharT, _Traits, _Allocator>'
   34 |                 q = s.p1 +(s.p2 - s.p1)*(prod/((s.p1.x-s.p2.x)*(s.p1.x - s.p2.x)+ (s.p1.y - s.p2.y)*(s.p1.y - s.p2.y)));
      |                                                                                                                       ^
/usr/include/c++/14/bits/basic_string.h:3652:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> std::__cxx11::basic_string<_CharT, _Traits, _Allocator> std::operator+(const __cxx11::basic_string<_CharT, _Traits, _Allocator>&, const _CharT*)'
 3652 |     operator+(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3652:5: note:   template argument deduction/substitution failed:
a.cc:34:119: note:   'Point' is not derived from 'const std::__cxx11::basic_string<_CharT, _Traits, _Allocator>'
   34 |                 q = s.p1 +(s.p2 - s.p1)*(prod/((s.p1.x-s.p2.x)*(s.p1.x - s.p2.x)+ (s.p1.y - s.p2.y)*(s.p1.y - s.p2.y)));
      |                                                                                                                       ^
/usr/include/c++/14/bits/basic_string.h:3670:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> std::__cxx11::basic_string<_CharT, _Traits, _Allocator> std::operator+(const __cxx11::basic_string<_CharT, _Traits, _Allocator>&, _CharT)'
 3670 |     operator+(const basic_string<_CharT, _Traits, _Alloc>& __lhs, _CharT __rhs)
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3670:5: note:   template argument deduction/substitution failed:
a.cc:34:119: note:   'Point' is not derived from 'const std::__cxx11::basic_string<_CharT, _Traits, _Allocator>'
   34 |                 q = s.p1 +(s.p2 - s.p1)*(prod/((s.p1.x-s.p2.x)*(s.p1.x - s.p2.x)+ (s.p1.y - s.p2.y)*(s.p1.y - s.p2.y)));
      |                                                                                                                       ^
/usr/include/c++/14/bits/basic_string.h:3682:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> std::__cxx11::basic_string<_CharT, _Traits, _Allocator> std::operator+(__cxx11::basic_string<_CharT, _Traits, _Allocator>&&, const __cxx11::basic_string<_CharT, _Traits, _Allocator>&)'
 3682 |     operator+(basic_string<_CharT, _Traits, _Alloc>&& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3682:5: note:   template argument deduction/substitution failed:
a.cc:34:119: note:   'Point' is not derived from 'std::__cxx11::basic_string<_CharT, _Traits, _Allocator>'
   34 |                 q = s.p1 +(s.p2 - s.p1)*(prod/((s.p1.x-s.p2.x)*(s.p1.x - s.p2.x)+ (s.p1.y - s.p2.y)*(s.p1.y - s.p2.y)));
      |                                                                                                                       ^
/usr/include/c++/14/bits/basic_string.h:3689:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> std::__cxx11::basic_string<_CharT, _Traits, _Allocator> std::operator+(const __cxx11::basic_string<_CharT, _Traits, _Allocator>&, __cxx11::basic_string<_CharT, _Traits, _Allocator>&&)'
 3689 |     operator+(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3689:5: note:   template argument deduction/substitution failed:
a.cc:34:119: note:   'Point' is not derived from 'const std::__cxx11::basic_string<_CharT, _Traits, _Allocator>'
   34 |                 q = s.p1 +(s.p2 - s.p1)*(prod/((s.p1.x-s.p2.x)*(s.p1.x - s.p2.x)+ (s.p1.y - s.p2.y)*(s.p1.y - s.p2.y)));
      |                                                                                                                       ^
/usr/include/c++/14/bits/basic_string.h:3696:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> std::__cxx11::basic_string<_CharT, _Traits, _Allocator> std::operator+(__cxx11::basic_string<_CharT, _Traits, _Allocator>&&, __cxx11::basic_string<_CharT, _Traits, _Allocator>&&)'
 3696 |     operator+(basic_string<_CharT, _Traits, _Alloc>&& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3696:5: note:   template argument deduction/substitution failed:
a.cc:34:119: note:   'Point' is not derived from 'std::__cxx11::basic_string<_CharT, _Traits, _Allocator>'
   34 |                 q = s.p1 +(s.p2 - s.p1)*(prod/((s.p1.x-s.p2.x)*(s.p1.x - s.p2.x)+ (s.p1.y - s.p2.y)*(s.p1.y - s.p2.y)));
      |                                                                                                                       ^
/usr/include/c++/14/bits/basic_string.h:3719:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> std::__cxx11::basic_string<_CharT, _Traits, _Allocator> std::operator+(const _CharT*, __cxx11::basic_string<_CharT, _Traits, _Allocator>&&)'
 3719 |     operator+(const _CharT* __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3719:5: note:   template argument deduction/substitution failed:
a.cc:34:119: not