Language: C++

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

int main() {
    int i, j;

    int h, w;
    cin >> h >> w;
    
    vector<vector<char>> a(h, vector<char>(w));
    for (i = 0; i < h; i++) {
        for (j = 0; j < w; j++) {
            cin >> a[i][j];
        }
    }
    
    vector<vector<char>> b(h + 2, vector<char>(w + 2), '#');
    for (i = 0; i < h; i++) {
        for (j = 0; j < w; j++) {
            b[i + 1][j + 1] = a[i][j];
        }
    }
    
    for (i = 0; i < h + 2; i++) {
        for (j = 0; j < w + 2; j++) {
            cout << b[i][j];
        }
        cout << endl;
    }
}

Compiler output:
a.cc: In function 'int main()':
a.cc:17:59: error: no matching function for call to 'std::vector<std::vector<char> >::vector(int, std::vector<char>, char)'
   17 |     vector<vector<char>> b(h + 2, vector<char>(w + 2), '#');
      |                                                           ^
In file included from /usr/include/c++/14/vector:66,
                 from /usr/include/c++/14/functional:64,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:53,
                 from a.cc:1:
/usr/include/c++/14/bits/stl_vector.h:707:9: note: candidate: 'template<class _InputIterator, class> std::vector<_Tp, _Alloc>::vector(_InputIterator, _InputIterator, const allocator_type&) [with <template-parameter-2-2> = _InputIterator; _Tp = std::vector<char>; _Alloc = std::allocator<std::vector<char> >]'
  707 |         vector(_InputIterator __first, _InputIterator __last,
      |         ^~~~~~
/usr/include/c++/14/bits/stl_vector.h:707:9: note:   template argument deduction/substitution failed:
a.cc:17:59: note:   deduced conflicting types for parameter '_InputIterator' ('int' and 'std::vector<char>')
   17 |     vector<vector<char>> b(h + 2, vector<char>(w + 2), '#');
      |                                                           ^
/usr/include/c++/14/bits/stl_vector.h:678:7: note: candidate: 'std::vector<_Tp, _Alloc>::vector(std::initializer_list<_Tp>, const allocator_type&) [with _Tp = std::vector<char>; _Alloc = std::allocator<std::vector<char> >; allocator_type = std::allocator<std::vector<char> >]'
  678 |       vector(initializer_list<value_type> __l,
      |       ^~~~~~
/usr/include/c++/14/bits/stl_vector.h:678:7: note:   candidate expects 2 arguments, 3 provided
/usr/include/c++/14/bits/stl_vector.h:659:7: note: candidate: 'std::vector<_Tp, _Alloc>::vector(std::vector<_Tp, _Alloc>&&, std::__type_identity_t<_Alloc>&) [with _Tp = std::vector<char>; _Alloc = std::allocator<std::vector<char> >; std::__type_identity_t<_Alloc> = std::allocator<std::vector<char> >]'
  659 |       vector(vector&& __rv, const __type_identity_t<allocator_type>& __m)
      |       ^~~~~~
/usr/include/c++/14/bits/stl_vector.h:659:7: note:   candidate expects 2 arguments, 3 provided
/usr/include/c++/14/bits/stl_vector.h:640:7: note: candidate: 'std::vector<_Tp, _Alloc>::vector(std::vector<_Tp, _Alloc>&&, const allocator_type&, std::false_type) [with _Tp = std::vector<char>; _Alloc = std::allocator<std::vector<char> >; allocator_type = std::allocator<std::vector<char> >; std::false_type = std::false_type]'
  640 |       vector(vector&& __rv, const allocator_type& __m, false_type)
      |       ^~~~~~
/usr/include/c++/14/bits/stl_vector.h:640:23: note:   no known conversion for argument 1 from 'int' to 'std::vector<std::vector<char> >&&'
  640 |       vector(vector&& __rv, const allocator_type& __m, false_type)
      |              ~~~~~~~~~^~~~
/usr/include/c++/14/bits/stl_vector.h:635:7: note: candidate: 'std::vector<_Tp, _Alloc>::vector(std::vector<_Tp, _Alloc>&&, const allocator_type&, std::true_type) [with _Tp = std::vector<char>; _Alloc = std::allocator<std::vector<char> >; allocator_type = std::allocator<std::vector<char> >; std::true_type = std::true_type]'
  635 |       vector(vector&& __rv, const allocator_type& __m, true_type) noexcept
      |       ^~~~~~
/usr/include/c++/14/bits/stl_vector.h:635:23: note:   no known conversion for argument 1 from 'int' to 'std::vector<std::vector<char> >&&'
  635 |       vector(vector&& __rv, const allocator_type& __m, true_type) noexcept
      |              ~~~~~~~~~^~~~
/usr/include/c++/14/bits/stl_vector.h:624:7: note: candidate: 'std::vector<_Tp, _Alloc>::vector(const std::vector<_Tp, _Alloc>&, std::__type_identity_t<_Alloc>&) [with _Tp = std::vector<char>; _Alloc = std::allocator<std::vector<char> >; std::__type_identity_t<_Alloc> = std::allocator<std::vector<char> >]'
  624 |       vector(const vector& __x, const __type_identity_t<allocator_type>& __a)
      |       ^~~~~~
/usr/include/c++/14/bits/stl_vector.h:624:7: note:   candidate expects 2 arguments, 3 provided
/usr/include/c++/14/bits/stl_vector.h:620:7: note: candidate: 'std::vector<_Tp, _Alloc>::vector(std::vector<_Tp, _Alloc>&&) [with _Tp = std::vector<char>; _Alloc = std::allocator<std::vector<char> >]'
  620 |       vector(vector&&) noexcept = default;
      |       ^~~~~~
/usr/include/c++/14/bits/stl_vector.h:620:7: note:   candidate expects 1 argument, 3 provided
/usr/include/c++/14/bits/stl_vector.h:601:7: note: candidate: 'std::vector<_Tp, _Alloc>::vector(const std::vector<_Tp, _Alloc>&) [with _Tp = std::vector<char>; _Alloc = std::allocator<std::vector<char> >]'
  601 |       vector(const vector& __x)
      |       ^~~~~~
/usr/include/c++/14/bits/stl_vector.h:601:7: note:   candidate expects 1 argument, 3 provided
/usr/include/c++/14/bits/stl_vector.h:569:7: note: candidate: 'std::vector<_Tp, _Alloc>::vector(size_type, const value_type&, const allocator_type&) [with _Tp = std::vector<char>; _Alloc = std::allocator<std::vector<char> >; size_type = long unsigned int; value_type = std::vector<char>; allocator_type = std::allocator<std::vector<char> >]'
  569 |       vector(size_type __n, const value_type& __value,
      |       ^~~~~~
/usr/include/c++/14/bits/stl_vector.h:570:36: note:   no known conversion for argument 3 from 'char' to 'const std::vector<std::vector<char> >::allocator_type&' {aka 'const std::allocator<std::vector<char> >&'}
  570 |              const allocator_type& __a = allocator_type())
      |              ~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/stl_vector.h:556:7: note: candidate: 'std::vector<_Tp, _Alloc>::vector(size_type, const allocator_type&) [with _Tp = std::vector<char>; _Alloc = std::allocator<std::vector<char> >; size_type = long unsigned int; allocator_type = std::allocator<std::vector<char> >]'
  556 |       vector(size_type __n, const allocator_type& __a = allocator_type())
      |       ^~~~~~
/usr/include/c++/14/bits/stl_vector.h:556:7: note:   candidate expects 2 arguments, 3 provided
/usr/include/c++/14/bits/stl_vector.h:542:7: note: candidate: 'std::vector<_Tp, _Alloc>::vector(const allocator_type&) [with _Tp = std::vector<char>; _Alloc = std::allocator<std::vector<char> >; allocator_type = std::allocator<std::vector<char> >]'
  542 |       vector(const allocator_type& __a) _GLIBCXX_NOEXCEPT
      |       ^~~~~~
/usr/include/c++/14/bits/stl_vector.h:542:7: note:   candidate expects 1 argument, 3 provided
/usr/include/c++/14/bits/stl_vector.h:531:7: note: candidate: 'std::vector<_Tp, _Alloc>::vector() [with _Tp = std::vector<char>; _Alloc = std::allocator<std::vector<char> >]'
  531 |       vector() = default;
      |       ^~~~~~
/usr/include/c++/14/bits/stl_vector.h:531:7: note:   candidate expects 0 arguments, 3 provided