Language: C++

    #include<iostream>
    #include<vector>
    #include<string> 
    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:6:7: 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:7:7: error: 'vector' was not declared in this scope
    7 |       vector <char>c;
      |       ^~~~~~
a.cc:7:7: 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:7:15: error: expected primary-expression before 'char'
    7 |       vector <char>c;
      |               ^~~~
a.cc:9:9: error: 'string' was not declared in this scope
    9 |         string s;
      |         ^~~~~~
a.cc:9:9: 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:10:14: error: 's' was not declared in this scope
   10 |         cin>>s;
      |              ^
a.cc:11:13: error: 'j' was not declared in this scope
   11 |         for(j=0;j<b;j++0)
      |             ^
a.cc:11:24: error: expected ')' before numeric constant
   11 |         for(j=0;j<b;j++0)
      |            ~           ^
      |                        )
a.cc:11:25: error: expected ';' before ')' token
   11 |         for(j=0;j<b;j++0)
      |                         ^
      |                         ;
a.cc:15:13: error: 'j' was not declared in this scope
   15 |         for(j=0;j<b;j++){
      |             ^
a.cc:16:11: 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:16:17: error: 'c' was not declared in this scope
   16 |           cout<<c[i][j];
      |                 ^
a.cc:18:7: 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:18:13: 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:19:11: error: 'j' was not declared in this scope
   19 |       for(j=0;j<b;j++){
      |           ^
a.cc:20:17: error: 'c' was not declared in this scope
   20 |           cout<<c[i][j];
      |                 ^
a.cc: At global scope:
a.cc:24:5: error: expected unqualified-id before 'return'
   24 |     return 0;
      |     ^~~~~~
a.cc:25:5: error: expected declaration before '}' token
   25 |     }
      |     ^