I've searched for this and found a few topics , usually they used a function normalize and using simple vector subtracting which is ok , but how should I do it in sfml ? Instead of using:

Movement = p.position() - m.position();

p is the player and m is the monster

I used something like this to move on a straight line:

sf::Vector2f Tail(0,0);
    if((mPlayer.getPosition().y - mMonster.GetInstance().getPosition().y) >= (mPlayer.getPosition().x - mMonster.GetInstance().getPosition().x)){
        //sf::Vector2f Tail(0,0);
        Tail.x = mPlayer.getPosition().x - mMonster.GetInstance().getPosition().x;

    }
    else if((mPlayer.getPosition().y - mMonster.GetInstance().getPosition().y) <= (mPlayer.getPosition().x - mMonster.GetInstance().getPosition().x)){
        //sf::Vector2f Tail(0,0);
        Tail.y = mPlayer.getPosition().y - mMonster.GetInstance().getPosition().y;

    }

    if(!MonsterCollosion())
    mMonster.Move(Tail * (TimePerFrame.asSeconds() * 1/2 ) );

It works ok if the the height = the width for the game window, although I think it's not the best looking game when it comes to a moving monster, since it starts fast and then it gets slower

so what do you guys advise me to do ?