c++ - How to detect collision between two directed object?

I'm currently writing a game which is like Battle City game. But right now I'm facing a trouble involved to checking collision between two objects. This is the code that I wrote:

//-------------------------------------------------------------------------------------------
//  check collision between a tank and another object
//
bool GameController::checkTankMeetsObject(Tank tank, GameObject ob)
{
    int obX = ob.getCoord().getX();
    int obY = ob.getCoord().getY();

    // calculate area of obstacle: bottom left (X1, Y1), top right (X2, Y2)
    int obX1 = obX - SQUARESIZE / 2;

    int obX2 = obX + SQUARESIZE / 2;
    int obY1 = obY - SQUARESIZE / 2;
    int obY2 = obY + SQUARESIZE / 2;

    int tankX = tank.getCoord().getX();
    int tankY = tank.getCoord().getY();

    switch (tank.getDir())
    {
    case UP:

        if ((tankX < obX2 + SQUARESIZE / 2 && tankX > obX1 - SQUARESIZE / 2) &&
            (tankY + SQUARESIZE / 2 > obY1 && tankY + SQUARESIZE / 2 < obY2))
            return true;
        break;

    case DOWN:
        if ((tankX < obX2 + SQUARESIZE / 2 && tankX > obX1 - SQUARESIZE / 2) &&
            (tankY - SQUARESIZE / 2 > obY1 && tankY - SQUARESIZE / 2 < obY2))
            return true;
        break;


    case LEFT:
        if ((tankX - SQUARESIZE / 2 < obX2 && tankX - SQUARESIZE / 2 > obX1) &&
            (tankY > obY1 - SQUARESIZE / 2 && tankY < obY2 + SQUARESIZE / 2))
            return true;
        break;

    case RIGHT:
        if ((tankX + SQUARESIZE / 2 < obX2 && tankX + SQUARESIZE / 2 > obX1) &&
            (tankY > obY1 - SQUARESIZE / 2 && tankY < obY2 + SQUARESIZE / 2))

            return true;
        break;
    }

    return false;
}

This code does well with normal circumstance, but in special ones like which I describe below, it doesn't work.

The white squares are obstacles and the grey square is the tank. Current direction of the tank is RIGHT. In this situation, I can not move the tank RIGHT or LEFT, only direction I can go is DOWN. Is there any solution to optimize my code?