Why do you want to convert sf::Rect<float> to simple float?
Just use
yourRect.contains(MousePosition) == bool
You should create your own thread unless it's really about exactly the same thing and use the [code=cpp][/code] tags.
Next you should gather more experience with C++ and compiler errors if you can't figure out what the error message means... ;)
else if (!button[0].getGlobalBounds().contains(sf::Mouse::getPosition(updatetarget).x, sf::Mouse::getPosition(updatetarget).y)
&& (button[0].getColor() == sf::Color::White)
You never close the if( statement.