/* Chest.cs */
public static int FindChest(int X, int Y)
{
    for (int i = 0; i < 0x3e8; i++)
    {
        if (((Main.chest[i] != null) && (Main.chest[i].x == X)) && (Main.chest[i].y == Y))
        {
            return i;
        }
    }
    return -1;
}

/* Player.cs */
if (!flag8)
{
    num66 = Chest.FindChest(num64, y);
}
...
if (num66 == this.chest)
{
    this.chest = -1;
    Main.PlaySound(11, -1, -1, 1);
}
else if ((num66 != this.chest) && (this.chest == -1))
{
    this.chest = num66;
    Main.playerInventory = true;
    Main.PlaySound(10, -1, -1, 1);
    this.chestX = num64;
    this.chestY = y;
}
else
{
    this.chest = num66;
    Main.playerInventory = true;
    Main.PlaySound(12, -1, -1, 1);
    this.chestX = num64;
    this.chestY = y;
}