During a game play i have become to a vampire witch means that i cant visit cities. Is some one know what should i do to avoid becoming a vampire or is ther some qure from this ?

If you get attacked by townspeople, lower your vampirism stage by drinking blood from sleeping people. If you want to cure the whole disease, do a side quest in Morthal. You can get it by asking rumors in the town.

There is a quest to cure the condition but to be able to visit cities find a sleeping person somewhere and feed on him/her so it reverts your vampirism back to stage 1 and keep doing that every day or two until you manage to get the condition cured...

You have to feed on blood to don't look suspicious.
And you can always cure the pre-vampire disease by visting a shrine.

You can visit this site for more information: http://www.uesp.net/wiki/Skyrim:Vampirism

Oh, I see you're new to the forum. Welcome! Have a http://images.uesp.net/c/c4/Fishystick.jpg!

I honestly will never understand how people can accidentally become vampires, you'd think the big red screen flash with the text "You feel weak in the sun" or whatever would give a clue something is wrong. But anyways, feeding on sleeping NPC's will revert your vampire level and let you walk around in cities. Head to any Inn and ask the person at the bar about rumours. You will always get the quest to cure yourself. If you are having trouble take advantage of the powers to to calm people and become invisible to feed on someone sleeping.
But yea, visit the UESP to learn everything you need, it's very helpful.

Doesnt becoming a werewolf cure you of Vampirism?

Thats when they realise yea? Most people probably got into a fight with a vampire and didnt check their active effects or something, its quite easy to become one if you're against vampires