What is the difference between dystopian and post apocalyptic literature?
i want to know the main different points.also can we consider post apocalyptic as science fiction literature where dystopian is not?
There isn't a clear difference. Certain dystopic societies could occur in a post-apocalyptic world. And certain (or most) apocalyptic societies could be considered dystopian. The main difference, especially in literature, is that dystopian societies are often the result of revolutions or the effects of the illusion of progress and other intended means of improvement. So, dystopias are often the unfortunate result of well-meaning, albeit misguided attempts at progress and social evolution. Post-apocalyptic societies are the aftermath of nuclear war, plague, or religious 'end of days'/Book of Revelation types of scenarios.
In short, since post-apocalyptic societies are all at the end of civilization, they are necessarily dystopias. But not all dystopias are post-apocalyptic. For instance, novels like 1984 and Brave New World are not really post-apocalyptic. They are societies evolved from the progress of increasing governmental control.
Apocalypticism is often due to war (which is humanity's folly), plague, or some spiritual end/revelation. Dystopias, in literature, and movies are often the result of misguided societal revolutions: and this is from the left or right - with the pursuit of either extreme, the result is often illustrated as leading to fundamentalism and subsequently, a narrow-minded view of culture, which leads to too much control or anarchy.
Examples of post-apocalyptic in literature and film: The Stand, 2012, War of the Worlds, 28 Days Later, I am Legend.
List of dystopias: Brave New World, Swastika Night, 1984, The Handmaid's Tale.
My best idea of how to differentiate post-apocalyptic and dystopian is that dystopian societies are usually humanity's fault and post-apocalyptic can be humanity's fault (nuclear war), but is often the result of natural causes or spiritual intervention.
The movie WALL-E is an example of both. You could probably argue that BNW and 1984 are also post-apocalyptic, but given that the consistent difference between dystopic/post-apocalyptic is human-cause/natural or divine intervention, I tend to call them dystopic. Still, it is open to interpretation. I'd consider the movie Blade Runner to be both, Shirley Jackson's "The Lottery" to be dystopian, V for Vendetta and Fahrenheit 451 could be both and on we go.