Language: C++

#include <bits/stdc++.h>
using namspace std;

int main(void)
{
  int H, W;
  cin >> H >> W;
  string S[50];
  
  for (int i=0;i<H;i++){
    cin >> S[i];
  }
  
  bool can = true;
  int dy[4] = {0, 1, 0, -1};
  int dx[4] = {1, 0, -1, 0};
  
  for (int i=0;i<H;i++){
    for (int j=0;j<W;j++){
      if (S[i][j] != '#') continue;
      
      for (int k=0;k<4;k++){
        int ni = i + dy[k];
        int nj = j + dx[k];
        
        if (S[ni][nj] == '#') break;
      }
      if (k == 4){
        can = false;
      }
    }
    if (!can) break;
  }
  
  if (can){
    cout << "Yes" << endl;
  }else {
    cout << "No" << endl;
  }
  
  return 0;
}

Compiler output:
a.cc:2:7: error: expected nested-name-specifier before 'namspace'
    2 | using namspace std;
      |       ^~~~~~~~
a.cc: In function 'int main()':
a.cc:7:3: error: 'cin' was not declared in this scope; did you mean 'std::cin'?
    7 |   cin >> H >> W;
      |   ^~~
      |   std::cin
In file included from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:146,
                 from a.cc:1:
/usr/include/c++/14/iostream:62:18: note: 'std::cin' declared here
   62 |   extern istream cin;           ///< Linked to standard input
      |                  ^~~
a.cc:8:3: error: 'string' was not declared in this scope
    8 |   string S[50];
      |   ^~~~~~
a.cc:8:3: note: suggested alternatives:
In file included from /usr/include/c++/14/string:41,
                 from /usr/include/c++/14/bitset:52,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:52:
/usr/include/c++/14/bits/stringfwd.h:77:33: note:   'std::string'
   77 |   typedef basic_string<char>    string;
      |                                 ^~~~~~
/usr/include/c++/14/string:76:11: note:   'std::pmr::string'
   76 |     using string    = basic_string<char>;
      |           ^~~~~~
a.cc:11:12: error: 'S' was not declared in this scope
   11 |     cin >> S[i];
      |            ^
a.cc:20:11: error: 'S' was not declared in this scope
   20 |       if (S[i][j] != '#') continue;
      |           ^
a.cc:26:13: error: 'S' was not declared in this scope
   26 |         if (S[ni][nj] == '#') break;
      |             ^
a.cc:28:11: error: 'k' was not declared in this scope
   28 |       if (k == 4){
      |           ^
a.cc:36:5: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
   36 |     cout << "Yes" << endl;
      |     ^~~~
      |     std::cout
/usr/include/c++/14/iostream:63:18: note: 'std::cout' declared here
   63 |   extern ostream cout;          ///< Linked to standard output
      |                  ^~~~
a.cc:36:22: error: 'endl' was not declared in this scope; did you mean 'std::endl'?
   36 |     cout << "Yes" << endl;
      |                      ^~~~
      |                      std::endl
In file included from /usr/include/c++/14/istream:41,
                 from /usr/include/c++/14/sstream:40,
                 from /usr/include/c++/14/complex:45,
                 from /usr/include/c++/14/ccomplex:39,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:127:
/usr/include/c++/14/ostream:744:5: note: 'std::endl' declared here
  744 |     endl(basic_ostream<_CharT, _Traits>& __os)
      |     ^~~~
a.cc:38:5: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
   38 |     cout << "No" << endl;
      |     ^~~~
      |     std::cout
/usr/include/c++/14/iostream:63:18: note: 'std::cout' declared here
   63 |   extern ostream cout;          ///< Linked to standard output
      |                  ^~~~
a.cc:38:21: error: 'endl' was not declared in this scope; did you mean 'std::endl'?
   38 |     cout << "No" << endl;
      |                     ^~~~
      |                     std::endl
/usr/include/c++/14/ostream:744:5: note: 'std::endl' declared here
  744 |     endl(basic_ostream<_CharT, _Traits>& __os)
      |     ^~~~