How much cost me for food in vienna for six days?

im planning to go to prague for six days and after take a train to vienna for another six days .could anyone tell me how much cost me for those days just for foods.
remember just for foods nothing els.
thank you.

It depends how and what you want to eat. If you are a fast food fan you may use McDonalds for 1 Euro per cheeseburger or hamburger. However, I would suggest you enjoy the Austrian kitchen.
Especially in Vienna you will find a huge range of different restaurants. Avoid the main shopping areas and the 1st district and look out for small restaurants. You can have lunch or dinner for 5 - 10 Euros easily if you use the menue of the day. Be aware that the typical Viennese "Gasthaus" where the locals go has no english menue...
If you go to higher-priced restaurants you may pay up to 30 Euros for a dinner but it is not necessary to go to these places.
Another option is to use the "Wuerstelstand", those are booths selling hot sausages and you can find them all over the city - that's our Austrian kind of fast food.
You also can save money if you go to chinese and italian restaurants, they are mostly cheaper than others. Most of the restaurants and gasthauses have their menue displayed in front of the door, so check the prices before you order.
Of course, you can also buy bread and meet or cheese in a regular grocery shop - up to you!
Please note that all prices in the menues are including all the taxes, thats different to the US and other states. However, if you are satisfied with the service the waiters are always happy with tip. Consider 10 percent as maximum if you like.
To answer your question at a point: calculate 150 Euros for 6 days for food, that would do it...
By the way - I did not calculate beer and wine, which you should taste in Vienna as well!
And another point - think of coming to Salzburg at least for 2 days, you will love it!