Language: C++

#include<iostream>
#include<vector>

int main(){
  int a,b,i;
  cin>>a>>b;
  vector <char>c;
  for(i=0;i<a;i++){
    string s;
    cin>>s;
    for(j=0;j<b;j++0)
      c[i][j]=s[j];
  }
  for(i=0;i<a;i++)
    for(j=0;j<b;j++){
      cout<<c[i][j];
    }
  cout<<endl;
  for(j=0;j<b;j++){
      cout<<c[i][j];
    }
  cout<<endl;
}
return 0;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:6:3: error: 'cin' was not declared in this scope; did you mean 'std::cin'?
    6 |   cin>>a>>b;
      |   ^~~
      |   std::cin
In file included 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:7:3: error: 'vector' was not declared in this scope
    7 |   vector <char>c;
      |   ^~~~~~
a.cc:7:3: note: suggested alternatives:
In file included from /usr/include/c++/14/vector:66,
                 from a.cc:2:
/usr/include/c++/14/bits/stl_vector.h:428:11: note:   'std::vector'
  428 |     class vector : protected _Vector_base<_Tp, _Alloc>
      |           ^~~~~~
/usr/include/c++/14/vector:93:13: note:   'std::pmr::vector'
   93 |       using vector = std::vector<_Tp, polymorphic_allocator<_Tp>>;
      |             ^~~~~~
a.cc:7:11: error: expected primary-expression before 'char'
    7 |   vector <char>c;
      |           ^~~~
a.cc:9:5: error: 'string' was not declared in this scope
    9 |     string s;
      |     ^~~~~~
a.cc:9:5: note: suggested alternatives:
In file included from /usr/include/c++/14/iosfwd:41,
                 from /usr/include/c++/14/ios:40,
                 from /usr/include/c++/14/ostream:40,
                 from /usr/include/c++/14/iostream:41:
/usr/include/c++/14/bits/stringfwd.h:77:33: note:   'std::string'
   77 |   typedef basic_string<char>    string;
      |                                 ^~~~~~
In file included 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:
/usr/include/c++/14/string:76:11: note:   'std::pmr::string'
   76 |     using string    = basic_string<char>;
      |           ^~~~~~
a.cc:10:10: error: 's' was not declared in this scope
   10 |     cin>>s;
      |          ^
a.cc:11:9: error: 'j' was not declared in this scope
   11 |     for(j=0;j<b;j++0)
      |         ^
a.cc:11:20: error: expected ')' before numeric constant
   11 |     for(j=0;j<b;j++0)
      |        ~           ^
      |                    )
a.cc:11:21: error: expected ';' before ')' token
   11 |     for(j=0;j<b;j++0)
      |                     ^
      |                     ;
a.cc:15:9: error: 'j' was not declared in this scope
   15 |     for(j=0;j<b;j++){
      |         ^
a.cc:16:7: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
   16 |       cout<<c[i][j];
      |       ^~~~
      |       std::cout
/usr/include/c++/14/iostream:63:18: note: 'std::cout' declared here
   63 |   extern ostream cout;          ///< Linked to standard output
      |                  ^~~~
a.cc:16:13: error: 'c' was not declared in this scope
   16 |       cout<<c[i][j];
      |             ^
a.cc:18:3: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
   18 |   cout<<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:18:9: error: 'endl' was not declared in this scope; did you mean 'std::endl'?
   18 |   cout<<endl;
      |         ^~~~
      |         std::endl
/usr/include/c++/14/ostream:744:5: note: 'std::endl' declared here
  744 |     endl(basic_ostream<_CharT, _Traits>& __os)
      |     ^~~~
a.cc:19:7: error: 'j' was not declared in this scope
   19 |   for(j=0;j<b;j++){
      |       ^
a.cc:20:13: error: 'c' was not declared in this scope
   20 |       cout<<c[i][j];
      |             ^
a.cc: At global scope:
a.cc:24:1: error: expected unqualified-id before 'return'
   24 | return 0;
      | ^~~~~~
a.cc:25:1: error: expected declaration before '}' token
   25 | }
      | ^