Tic Tac Toe in C++

I'll just review what you have here, although something like this would work better with classes (you could always attempt this implementation later).

• Your vector isn't quite grid-like as it's only one-dimensional. It may also be why Display() is a bit confusing, which shouldn't be the case with a 2D structure.

  Either way, you just need an std::array since the board's size is fixed:

  std::array<std::array<char, 3>, 3> grid;
  

  You first need to include <array>, and you can then remove <vector>.

• In bool Used(), this:

  if(grid[position] == '-')
      return false;
  else
      return true;
  

  can simply become this:

  return !(grid[position] == '-');
  

  The statement already gives a conditional result, so you just have to return it.

  Also, you don't need to pass position by const& as it's a native type. Just pass by value, with const if you want to be safe.

• Don't just list variables at the start of Turn() (or in general). Declare or initialize them as close to their use as possible.

  For instance, here's what it should be for the user input portion:

  std::cout << "Row(1,2,3): ";
  int row;
  std::cin >> row;
  std::cout << player << ": Column(A,B,C): ";
  char column = 0;
  std::cin >> column;
  

  Side-note: row and column don't need be initialized; they can just be declared.

  Consider having input validation in case the user inputs a valid board spot, otherwise the program will stop working and the game will have to be restarted.

  You could also simplify the function and the input validation by using either letters or numbers for both row and column. Using different ones makes the code and interface more confusing.

• This:

  while(check == true)
  

  is the same as this but more concise:

  while(check)
  

  For false, use !:

  while(!check)
  

• The while loop in main() is quite repetitive. You could just have a bool assigned to the winning player, then display that value in the winning (or losing) message after the loop.

  You should also have a way of choosing whether to start with X or O. Normally, someone will choose to go first, and they will choose their own symbol.

One improvement you can make is to only use one set of routines for each player. One simple way to do this is with a char array to represent each player:

int main()
{
    std::vector<char>grid(9,'-');
    char players[] = {'X','O'};
    int player = 1;
    while(true)
    {
        player = abs(player - 1);
        Display(grid);
        Turn(grid, players[player]);
        if(Win(grid, players[player]))
        {
            Display(grid);
            std::cout << "\n" << players[player] << " is the Winner!";
            break;
        }
    }
}

One other thing I noticed, is the logic for the turns isn't accurate. The columns and rows seem to get swapped.