Can you grab or delete between parentheses in vi/vim?

What about dib or di(.

It will delete the inner (...) block where the cursor is.

I love text-object motions and selections!

Various Motions: %

The % command jumps to the match of the item under the cursor. Position the cursor on the opening (or closing) paren and use y% for yanking or d% for deleting everything from the cursor to the matching paren.

This works because % is a "motion command", so it can be used anywhere vim expects such a command. From :help y:

["x]y{motion}       Yank {motion} text [into register x].  When no
                    characters are to be yanked (e.g., "y0" in column 1),
                    this is an error when 'cpoptions' includes the 'E'
                    flag.

By default, "item" includes brackets, braces, parens, C-style comments and various precompiler statements (#ifdef, etc.).

There is a plugin for "extended % matching" that you can find on the Vim homepage.

You can read the documentation on % and related motion commands by entering :help various-motions in command mode.

object-select

There is another set of motion commands that you can use in Visual mode to select various text objects.

To solve your specific problem you would do the following:

printf("%3.0f\t%6.1f\n", fahr, ((5.0/9.0) * (fahr-32)));
                                   ^

Let's say your cursor is positioned at ^. Enter the following sequence to select the part you are looking for:

v2a)

First v enters Visual mode, then you specify that you want to go 2 levels of parens up. Finally the a) selects "a block". After that you can use d or x to delete, etc.

If you don't want to include the outer parens, you can use "inner block" instead:

v2i)

See :help object-select for the complete list of related commands.