What constitutes a 'word' in vim?

Let's say we have the following in vim atm:

int main () {
    printf("hello");
    return 0;
}

In vim, w moves a word to the right, but what exactly constitutes a 'word'?

For example, if I have the cursor on p of printf, pressing w takes u to ( and pressing another w skips the " and puts the cursor on the h of hello. Why was the " skipped ?

Pressing another w now takes you to the other " before the ) and pressing another w takes you to the next line. Why where the ) and ; skipped?

And now the cursor is on the r of return. Pressing a w takes the cursor on 0 and pressing another w now takes the cursor on the ;. So in this case, the ; was not skipped unlike in the previous line. Why is this?

I hope I made my question clear enough but I'm just trying to understand how this all wor开发者_运维知识库ks.

From :help word:

A word consists of a sequence of letters, digits and underscores, or a sequence of other non-blank characters, separated with white space (spaces, tabs, ). This can be changed with the 'iskeyword' option. An empty line is also considered to be a word.

If your use capital W instead:

A WORD consists of a sequence of non-blank characters, separated with white space. An empty line is also considered to be a WORD.

In your example, w treats any sequence of non-keyword letters as a word too.

EDIT: The setting for virtualedit will influence this too: You must have it unset, because line-final punctuation is being skipped by w (add some whitespace to the end of the line to see the difference). If you set virtualedit=onemore the cursor will be able to stop one space beyond the end of the line, and line final punctuation won't ever be skipped.

From within vim, type

:help word-motions

You will get all the explanation you seek.