Should I change the structure of a sentence/add filler words to make sure that the sentence always starts with a capital letter?

Here is a quote from a book on C++ ("for", "while" and "do" are keywords in many languages, and in most languages they have to be in lower case. The C++ language is one of those.):

Simply put, algorithm names suggest what they do. "for", "while", and "do" don't.

One cannot write "For" instead of "for", because that would no longer refer to a well-known technical term, but to something else. Some attempts to fix this sentence would be:

The "for", "while", and "do" don't.

or:

The keywords "for", "while", and "do" don't.

or:

Use of "for", "while", or "do" does not.

Is this a good practice? Is this even an issue? What about other examples, such as starting sentence with a number, with a lower case letter in English or a foreign language, such as:

"l" looks a bit like "i". as opposed to something like: letter "l" looks a bit like "i".

Yes, I think it’s an issue. If you want the reader to get your point without being distracted by inconsequential issues of capitalization, you really have no choice but to add words at the beginning of the sentence. It is abnormal to start a sentence with a lowercase letter. Some readers will inevitably be distracted—perhaps even enough to put down the book, as you apparently did!

It would be quite silly to write something like this:

“L” looks a bit like “i”.

when what you mean is that a lowercase l looks a bit like i. Don’t wreck the meaning of your sentence in order to fix a style issue. Instead, write:

A lowercase “l” looks a bit like “i”.

(And as Cerberus notes, italics are better than quotes here, if you can get them.)

It would be distracting to capitalize the keyword for in a book about C++, since the keyword is never capitalized in C++ programs. The only answer is to recast the sentence:

The keywords for, while, and do don’t.

Yes, it is an issue; and, yes, that is excellent practice. A stylistically pleasing sentence should never start with a lower-case letter. Numbers are not as bad but should also be avoided if possible. Restructuring is often the key to good writing.

In most cases, it is acceptable to capitalize whatever is in the quote:

"L" looks a bit like "i".

Simply put, algorithm names suggest what they do. "For", "while", and "do" don't.

But I can understand why you should prefer restructuring, especially in the case of l/L, where shape matters (you could say lower-case "l" looks a bit like "i"). Note that italics would be better than quotation marks; in fact they usually are, if you're not actually quoting someone's words.

( Note that this is wrong:

*The "for", "while", and "do" don't.

You need something before "for", such as the "keywords" from your other example. )

Case 1: It should be: The keywords 'for','while','do' don't.

Case 2: It should be: 'L' looks a bit like 'i'. But 'l' doesn't look like 'a'.