Japanese Question: The difference between daro and darou?

>what does daro mean, without the u?

I am Japanese, so I speak Japanese without thinking gramatical reasons, but here is what I think:

daro is the same as darou. daro is more casual. That's it! It's a bit like "nothin'" instead of "nothing".

1. darou, is sometimes spelled as darō, in Roman letters (rōmaji). They are pronounced the same way. The "u" or the macron over the "o" simply double the length of the "o". Vowel length has phonemic meaning in Japanese (a doubled vowel counts as a different sound than a single vowel).

It can be used to express the idea of "I wonder", or with any other subject, when used as a question. It is not a literal translation though. It is a single word, neither of which means "I" or "wonder".

As a statement, it can express the idea of "probably". It expresses some doubt by the speaker. It is not a literal translation, though, of probably.

It is in the presumptive, plain, affirmative form of "da", one word for "be". darou -- is more literally a single word meaning "probably is/are".

The normal forms are "desu", and the presumptive: deshou. (all verbs and verbal adjectives come in plain and normal forms. Each one has specific uses).

It is normally written in hiragana (not in kanji).

2. daro (the "o" has normal length, it is not doubled), is the pronunciation of various words, with which I am less familiar. Most likely, if you saw this one, it was either a typo or written in a non-standard romanization system (darou, darō -- are the two normal spellings of #1 in standard rōmaji systems). However, if it was truly meant to be daro, we would need context, and ideally the actual Japanese spelling (kanji or kanji & hiragana combo) to identify its meaning.