Language: C++

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


int main(){

//入力を受け取る
int N ;
cin >> N ;

int M ;
cin >> M;

vector<int> S;
for(int i=0;i < 2M;i++){
    cin >> S.at(i)
}

//テストコード
for(int j=0;j<M; j++){
    cout << S.at(2j);
    cout << S.at(2j+1) << endl;
}



}

Compiler output:
a.cc: In function 'int main()':
a.cc:15:17: error: unable to find numeric literal operator 'operator""M'
   15 | for(int i=0;i < 2M;i++){
      |                 ^~
a.cc:16:19: error: expected ';' before '}' token
   16 |     cin >> S.at(i)
      |                   ^
      |                   ;
   17 | }
      | ~                  
a.cc:21:17: error: no matching function for call to 'std::vector<int>::at(__complex__ int)'
   21 |     cout << S.at(2j);
      |             ~~~~^~~~
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:1180:7: note: candidate: 'std::vector<_Tp, _Alloc>::reference std::vector<_Tp, _Alloc>::at(size_type) [with _Tp = int; _Alloc = std::allocator<int>; reference = int&; size_type = long unsigned int]'
 1180 |       at(size_type __n)
      |       ^~
/usr/include/c++/14/bits/stl_vector.h:1180:20: note:   no known conversion for argument 1 from '__complex__ int' to 'std::vector<int>::size_type' {aka 'long unsigned int'}
 1180 |       at(size_type __n)
      |          ~~~~~~~~~~^~~
/usr/include/c++/14/bits/stl_vector.h:1199:7: note: candidate: 'std::vector<_Tp, _Alloc>::const_reference std::vector<_Tp, _Alloc>::at(size_type) const [with _Tp = int; _Alloc = std::allocator<int>; const_reference = const int&; size_type = long unsigned int]'
 1199 |       at(size_type __n) const
      |       ^~
/usr/include/c++/14/bits/stl_vector.h:1199:20: note:   no known conversion for argument 1 from '__complex__ int' to 'std::vector<int>::size_type' {aka 'long unsigned int'}
 1199 |       at(size_type __n) const
      |          ~~~~~~~~~~^~~
a.cc:22:17: error: no matching function for call to 'std::vector<int>::at(__complex__ int)'
   22 |     cout << S.at(2j+1) << endl;
      |             ~~~~^~~~~~
/usr/include/c++/14/bits/stl_vector.h:1180:7: note: candidate: 'std::vector<_Tp, _Alloc>::reference std::vector<_Tp, _Alloc>::at(size_type) [with _Tp = int; _Alloc = std::allocator<int>; reference = int&; size_type = long unsigned int]'
 1180 |       at(size_type __n)
      |       ^~
/usr/include/c++/14/bits/stl_vector.h:1180:20: note:   no known conversion for argument 1 from '__complex__ int' to 'std::vector<int>::size_type' {aka 'long unsigned int'}
 1180 |       at(size_type __n)
      |          ~~~~~~~~~~^~~
/usr/include/c++/14/bits/stl_vector.h:1199:7: note: candidate: 'std::vector<_Tp, _Alloc>::const_reference std::vector<_Tp, _Alloc>::at(size_type) const [with _Tp = int; _Alloc = std::allocator<int>; const_reference = const int&; size_type = long unsigned int]'
 1199 |       at(size_type __n) const
      |       ^~
/usr/include/c++/14/bits/stl_vector.h:1199:20: note:   no known conversion for argument 1 from '__complex__ int' to 'std::vector<int>::size_type' {aka 'long unsigned int'}
 1199 |       at(size_type __n) const
      |          ~~~~~~~~~~^~~