Hide and unhide certain rows with certain value

I'm not so good with coding...

I need VBA macro for: a button that either hides or unhides rows when I click on it...
So, if rows are already hidden, then this button unhides them.
If those rows are not hidden, then it hides them.

The criteria what rows to hide/unhide is:
- Any rows that have the letter "r" within range ("C4:C350")

Please help!
Thanks!