Untitled

Why Removing item from list in this way is impossible?
public void RemoveFrmList(int ProdId)
        {
            int _index;
            foreach (Products item in BoughtItems)
            {
                if (item.ProductID == ProdId)
                {
                   _index = BoughtItems.IndexOf(item);
                }

            }
            BoughtItems.RemoveAt(_index);
        }

int _index;
foreach (Products item in BoughtItems)
{
   //Code here is not executed during runtime for reasons stated above.
}
BoughtItems.RemoveAt(_index); //error here because _index was not assigned!

int _index = -1;
foreach (...)
{
   //...
}
if (_index != -1){
   BoughtItems.RemoveAt(_index);
}
else
{
  //handle case if needed
}

public void RemoveFrmList(int ProdId)
{
    BoughtItems.RemoveAll( item => item.ProductID == ProdId );
}