If you really wanted to avoid the preposition, you could say that "the company's entire stock was sold...".
That said, "100% of the company's stock" is idiomatic and natural, and does not feel inconcise. English uses prepositions quite liberally, and they don't really make the sentence feel wordy.
*"The company's 100% stock" is ...
Your understanding may be correct. I believe your rephrasing, "a pointer to an automatic variable is returned", is very likely what the original writer meant. That, however, leaves the final part of the sentence, "in a previous function call," to be placed with 'a pointer' or with 'an automatic variable'.
Based on its location in the ...
The negation ("not") goes before all of the adjectives, including the article adjectives (a, the). He is not a funny guy.
For multiple negated adjectives, add the conjunction "nor": He is not a funny nor a nice guy.
We don't tend to use adjectives like this:
Either use an adjective with the opposite meaning
an unfunny guy
a humourless guy
Or use a clause
a guy who is not funny
None of these expressions are sentences. In a sentence you could say
That guy is not funny.
There is an older rule in English that forbids "splitting infinitives", i.e., putting any words between "to" and the verb word. The phrase "to thouroughly study" violates this rule.
However, this is extremely common usage, and some people will argue that it is necessary to split infinitives in some cases. I have not found such a ...
None of them seems exactly wrong but I would prefer the second one which flows more naturally when read aloud. Note that for the first example the comma between part and due is incorrect. The third one is the worst of the three to my ears as it makes you make a more definite pause twice at the commas.
In a comment John Lawler wrote:
For me precedes, and is the subject of, the conjoined infinitive clause to take Amy and go where no one will ever find us. That infinitive clause is the complement of The best thing would be, which comprises the beginning of the main clause. So the reason why for me is where it is is that it isn't saying who springing into ...