Does any CD players fit in all cars?

No, there's no single CD player that will fit *every* car. Car stereos (including those with CD players) come in a variety of standard sizes (most commonly double-DIN and single-DIN), but there are also many variations and non-standard sizes. Even within a standard size, the depth and surrounding features can vary, preventing a perfect fit. Furthermore, the mounting brackets and wiring harnesses are car-specific.