Assalamu alaikum
As I wrote in the Ramadan knights notes, fasting is one of the five pillars of Islam, a greatest of the deeds required in Islam. Leaving it without an excuse or breaking it without an excuse is a Major sin (kabirah) in Islam.
The person who did that ought to seek forgivenss from Allah and do tawbah by seeking istighfar, doing other good deeds etc.
Some scholars said the person should do qada whereas others said from ijtihad that there is no qada as it is not specified for such a case, and this is what I understand and Allah knows best.
You can find a support for the second opinion on a person who did not fast deliberately, at this link:
http://www.islamqa.com/en/ref/112102Wassalamu alaikum
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