Language: C++

#include <bits/stdc++.h>

using namespace std;

int main(){

	int H, W;

	cin >> H, W;

	int countH, countW;

	vector<vector<char>> table(H,vector<char>(W));

	for(int i = 0; i < H; i++){
		for(int j = 0; j < W; j++){

		cin >> table.at(i).at(j);

		}

	}

	vector<int> outW,outH;

	for(int i = 0; i < H; i++){
		for(int j = 0; j < W; j++){

			if(table.at(i).at(j) == '.')
				countW++;		//ある行iにおける'.'の数を計算

			if(table.at(j).at(i) =='.')
				countH++;		//ある列iにおける'.'の数を計算
		}

		if(countW != W)
			outW.push_back(i);		//全て'.'でない行だけを行列outWに追加

		if(countH != H)
			outH.push_back(i);		//全て'.'でない列だけを行列outHに追加
	

		countW = 0;
		countH = 0;

	}

	//outW, outHはそれぞれ出力していい行または列の集合

	for(int i = 0; i < outH.size();i++){
		for(int j = 0; j < outW.size();j++){

			if(table.at(outW.at(j)) == outW.size() )
				cout <<table.at(outH.at(i))at(outW.at(j)) <<endl;
			else
				cout <<table.at(outH.at(i))at(outW.at(j));
		}
	}

Compiler output:
a.cc: In function 'int main()':
a.cc:53:49: error: no match for 'operator==' (operand types are '__gnu_cxx::__alloc_traits<std::allocator<std::vector<char> >, std::vector<char> >::value_type' {aka 'std::vector<char>'} and 'std::vector<int>::size_type' {aka 'long unsigned int'})
   53 |                         if(table.at(outW.at(j)) == outW.size() )
      |                            ~~~~~~~~~~~~~~~~~~~~ ^~ ~~~~~~~~~~~
      |                                    |                        |
      |                                    |                        std::vector<int>::size_type {aka long unsigned int}
      |                                    __gnu_cxx::__alloc_traits<std::allocator<std::vector<char> >, std::vector<char> >::value_type {aka std::vector<char>}
In file included from /usr/include/c++/14/regex:68,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:181,
                 from a.cc:1:
/usr/include/c++/14/bits/regex.h:1103:5: note: candidate: 'template<class _BiIter> bool std::__cxx11::operator==(const sub_match<_BiIter>&, const sub_match<_BiIter>&)'
 1103 |     operator==(const sub_match<_BiIter>& __lhs, const sub_match<_BiIter>& __rhs)
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1103:5: note:   template argument deduction/substitution failed:
a.cc:53:62: note:   '__gnu_cxx::__alloc_traits<std::allocator<std::vector<char> >, std::vector<char> >::value_type' {aka 'std::vector<char>'} is not derived from 'const std::__cxx11::sub_match<_BiIter>'
   53 |                         if(table.at(outW.at(j)) == outW.size() )
      |                                                              ^
/usr/include/c++/14/bits/regex.h:1199:5: note: candidate: 'template<class _Bi_iter, class _Ch_traits, class _Ch_alloc> bool std::__cxx11::operator==(__sub_match_string<_Bi_iter, _Ch_traits, _Ch_alloc>&, const sub_match<_BiIter>&)'
 1199 |     operator==(const __sub_match_string<_Bi_iter, _Ch_traits, _Ch_alloc>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1199:5: note:   template argument deduction/substitution failed:
a.cc:53:62: note:   '__gnu_cxx::__alloc_traits<std::allocator<std::vector<char> >, std::vector<char> >::value_type' {aka 'std::vector<char>'} is not derived from 'std::__cxx11::__sub_match_string<_Bi_iter, _Ch_traits, _Ch_alloc>'
   53 |                         if(table.at(outW.at(j)) == outW.size() )
      |                                                              ^
/usr/include/c++/14/bits/regex.h:1274:5: note: candidate: 'template<class _Bi_iter, class _Ch_traits, class _Ch_alloc> bool std::__cxx11::operator==(const sub_match<_BiIter>&, __sub_match_string<_Bi_iter, _Ch_traits, _Ch_alloc>&)'
 1274 |     operator==(const sub_match<_Bi_iter>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1274:5: note:   template argument deduction/substitution failed:
a.cc:53:62: note:   '__gnu_cxx::__alloc_traits<std::allocator<std::vector<char> >, std::vector<char> >::value_type' {aka 'std::vector<char>'} is not derived from 'const std::__cxx11::sub_match<_BiIter>'
   53 |                         if(table.at(outW.at(j)) == outW.size() )
      |                                                              ^
/usr/include/c++/14/bits/regex.h:1366:5: note: candidate: 'template<class _Bi_iter> bool std::__cxx11::operator==(const typename std::iterator_traits<_Iter>::value_type*, const sub_match<_BiIter>&)'
 1366 |     operator==(typename iterator_traits<_Bi_iter>::value_type const* __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1366:5: note:   template argument deduction/substitution failed:
a.cc:53:62: note:   mismatched types 'const std::__cxx11::sub_match<_BiIter>' and 'std::vector<int>::size_type' {aka 'long unsigned int'}
   53 |                         if(table.at(outW.at(j)) == outW.size() )
      |                                                              ^
/usr/include/c++/14/bits/regex.h:1441:5: note: candidate: 'template<class _Bi_iter> bool std::__cxx11::operator==(const sub_match<_BiIter>&, const typename std::iterator_traits<_Iter>::value_type*)'
 1441 |     operator==(const sub_match<_Bi_iter>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1441:5: note:   template argument deduction/substitution failed:
a.cc:53:62: note:   '__gnu_cxx::__alloc_traits<std::allocator<std::vector<char> >, std::vector<char> >::value_type' {aka 'std::vector<char>'} is not derived from 'const std::__cxx11::sub_match<_BiIter>'
   53 |                         if(table.at(outW.at(j)) == outW.size() )
      |                                                              ^
/usr/include/c++/14/bits/regex.h:1534:5: note: candidate: 'template<class _Bi_iter> bool std::__cxx11::operator==(const typename std::iterator_traits<_Iter>::value_type&, const sub_match<_BiIter>&)'
 1534 |     operator==(typename iterator_traits<_Bi_iter>::value_type const& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1534:5: note:   template argument deduction/substitution failed:
a.cc:53:62: note:   mismatched types 'const std::__cxx11::sub_match<_BiIter>' and 'std::vector<int>::size_type' {aka 'long unsigned int'}
   53 |                         if(table.at(outW.at(j)) == outW.size() )
      |                                                              ^
/usr/include/c++/14/bits/regex.h:1613:5: note: candidate: 'template<class _Bi_iter> bool std::__cxx11::operator==(const sub_match<_BiIter>&, const typename std::iterator_traits<_Iter>::value_type&)'
 1613 |     operator==(const sub_match<_Bi_iter>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1613:5: note:   template argument deduction/substitution failed:
a.cc:53:62: note:   '__gnu_cxx::__alloc_traits<std::allocator<std::vector<char> >, std::vector<char> >::value_type' {aka 'std::vector<char>'} is not derived from 'const std::__cxx11::sub_match<_BiIter>'
   53 |                         if(table.at(outW.at(j)) == outW.size() )
      |                                                              ^
/usr/include/c++/14/bits/regex.h:2186:5: note: candidate: 'template<class _Bi_iter, class _Alloc> bool std::__cxx11::operator==(const match_results<_BiIter, _Alloc>&, const match_results<_BiIter, _Alloc>&)'
 2186 |     operator==(const match_results<_Bi_iter, _Alloc>& __m1,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:2186:5: note:   template argument deduction/substitution failed:
a.cc:53:62: note:   '__gnu_cxx::__alloc_traits<std::allocator<std::vector<char> >, std::vector<char> >::value_type' {aka 'std::vector<char>'} is not derived from 'const std::__cxx11::match_results<_BiIter, _Alloc>'
   53 |                         if(table.at(outW.at(j)) == outW.size() )
      |                                                              ^
In file included from /usr/include/c++/14/bits/stl_algobase.h:64,
                 from /usr/include/c++/14/algorithm:60,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:51:
/usr/include/c++/14/bits/stl_pair.h:1033:5: note: candidate: 'template<class _T1, class _T2> constexpr bool std::operator==(const pair<_T1, _T2>&, const pair<_T1, _T2>&)'
 1033 |     operator==(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_pair.h:1033:5: note:   template argument deduction/substitution failed:
a.cc:53:62: note:   '__gnu_cxx::__alloc_traits<std::allocator<std::vector<char> >, std::vector<char> >::value_type' {aka 'std::vector<char>'} is not derived from 'const std::pair<_T1, _T2>'
   53 |                         if(table.at(outW.at(j)) == outW.size() )
      |                                                              ^
In file included from /usr/include/c++/14/bits/stl_algobase.h:67:
/usr/include/c++/14/bits/stl_iterator.h:441:5: note: candidate: 'template<class _Iterator> constexpr bool std::operator==(const reverse_iterator<_Iterator>&, const reverse_iterator<_Iterator>&)'
  441 |     operator==(const reverse_iterator<_Iterator>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:441:5: note:   template argument deduction/substitution failed:
a.cc:53:62: note:   '__gnu_cxx::__alloc_traits<std::allocator<std::vector<char> >, std::vector<char> >::value_type' {aka 'std::vector<char>'} is not derived from 'const std::reverse_iterator<_Iterator>'
   53 |                         if(table.at(outW.at(j)) == outW.size() )
      |                                                              ^
/usr/include/c++/14/bits/stl_iterator.h:486:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr bool std::operator==(const reverse_iterator<_Iterator>&, const reverse_iterator<_IteratorR>&)'
  486 |     operator==(const reverse_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:486:5: note:   template argument deduction/substitution failed:
a.cc:53:62: note:   '__gnu_cxx::__alloc_traits<std::allocator<std::vector<char> >, std::vector<char> >::value_type' {aka 'std::vector<char>'} is not derived from 'const std::reverse_iterator<_Iterator>'
   53 |                         if(table.at(outW.at(j)) == outW.size() )
      |                                                              ^
/usr/include/c++/14/bits/stl_iterator.h:1667:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr bool std::operator==(const move_iterator<_IteratorL>&, const move_iterator<_IteratorR>&)'
 1667 |     operator==(const move_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1667:5: note:   template argument deduction/substitution failed:
a.cc:53:62: note:   '__gnu_cxx::__alloc_traits<std::allocator<std::vector<char> >, std::vector<char> >::value_type' {aka 'std::vector<char>'} is not derived from 'const std::move_iterator<_IteratorL>'
   53 |                         if(table.at(outW.at(j)) == outW.size() )
      |                                                              ^
/usr/include/c++/14/bits/stl_iterator.h:1737:5: note: candidate: 'template<class _Iterator> constexpr bool std::operator==(const move_iterator<_IteratorL>&, const move_iterator<_IteratorL>&)'
 1737 |     operator==(const move_iterator<_Iterator>& __x,
      |