Question

I’m trying to get a specific element inside of a vector.
For example,

Lets say I have a vector.

std::vector<Tile> TileList;

The Vector is of size MAP_HEIGHT = 30, MAP_WIDTH = 200
So its total size is MAP_HEIGHT * MAP_WIDTH = 6000.
I use a double nested for loop to iterate through and create a vector full of tiles.

for(int Y = 0; Y < MAP_HEIGHT; Y++)
{
   for(int X = 0; X < MAP_WIDTH; X++)
   {
        Tile TempTile;

        fscanf(FileHandle, "%d:%d ", &TempTile.TileID, &TempTile.TypeID);

        TileList.push_back(TempTile);

   }

}

Now my questions is lets say I iterate through

int ID = 0;

for(int Y = 0; Y < MAP_HEIGHT; Y++)
{
   for(int X = 0; X < MAP_WIDTH; X++)
   {
        TileList[ID].do stuff with it

        //Check for the tile above this tile
        // Find a way to calculate the ID of the tile above this tile
        int IDoftilabove = ID - do something;
        if(TileList[IDoftilabove].variable == TILE_SOMETHING)
        {
           do stuff
        }
       ID++;
    }

How do I calculate the ID of an element above(well technically before this ID) inside the vector based on the current element I’m on.

Illustration:
say i have a matrix 5×5,
Lets say my current ID is 8. so I am on the second row number 3.

1  2 *3* 4  5
1  2 (3) 4  5
1  2  3  4  5
1  2  3  4  5
1  2  3  4  5

Now I want the ID of the element in vector that is directly above me which is the ID 3, first row number 3. and this is just assuming the the MAP_WIDTH = 5 and the MAP_HEIGHT = 5.

Answer 1

8 - 5 = 3

Current – MAP_WIDTH = Above