Language: C++

#include<iostream>
#include<vector>
#include<algorithm>
int main(){
int N,i,sum=0;
cin>>N;
vector<int> a(N);
for(i=0;i<N;i++){
 cin>>a[i];
}
sort(a.begin(),a.end());
i=N-1;
if(N%2==0){
while(i-1>=0){
 sum=sum+a[i]-a[i-1];
 i=i-2;
}
cout<<sum<<endl;
}
if(N%2!=0){
while(i>=2){
  sum=sum+a[i]-a[i-1];
 i=i-2;
}
sum+=a[0];
cout<<sum<<endl;
}
return 0;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:6:1: error: 'cin' was not declared in this scope; did you mean 'std::cin'?
    6 | cin>>N;
      | ^~~
      | 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:7:1: error: 'vector' was not declared in this scope
    7 | vector<int> a(N);
      | ^~~~~~
a.cc:7:1: 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:7:8: error: expected primary-expression before 'int'
    7 | vector<int> a(N);
      |        ^~~
a.cc:9:7: error: 'a' was not declared in this scope
    9 |  cin>>a[i];
      |       ^
a.cc:11:6: error: 'a' was not declared in this scope
   11 | sort(a.begin(),a.end());
      |      ^
a.cc:11:1: error: 'sort' was not declared in this scope; did you mean 'std::sort'?
   11 | sort(a.begin(),a.end());
      | ^~~~
      | std::sort
In file included from /usr/include/c++/14/algorithm:86,
                 from a.cc:3:
/usr/include/c++/14/pstl/glue_algorithm_defs.h:296:1: note: 'std::sort' declared here
  296 | sort(_ExecutionPolicy&& __exec, _RandomAccessIterator __first, _RandomAccessIterator __last);
      | ^~~~
a.cc:18:1: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
   18 | cout<<sum<<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:18:12: error: 'endl' was not declared in this scope; did you mean 'std::endl'?
   18 | cout<<sum<<endl;
      |            ^~~~
      |            std::endl
In file included from /usr/include/c++/14/iostream:41:
/usr/include/c++/14/ostream:744:5: note: 'std::endl' declared here
  744 |     endl(basic_ostream<_CharT, _Traits>& __os)
      |     ^~~~
a.cc:26:1: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
   26 | cout<<sum<<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:26:12: error: 'endl' was not declared in this scope; did you mean 'std::endl'?
   26 | cout<<sum<<endl;
      |            ^~~~
      |            std::endl
/usr/include/c++/14/ostream:744:5: note: 'std::endl' declared here
  744 |     endl(basic_ostream<_CharT, _Traits>& __os)
      |     ^~~~